Full text of "Bulletin of the British Museum (Natural History) Geology Supplement"

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BRITISH AVONIAN (CARBONIFEROUS)

CONODONT FAUNAS, AND THEIR

VALUE IN LOCAL AND

INTERCONTINENTAL CORRELATION

F. H. T. RHODES,
R. L. AUSTIN, and E. C. DRUCE

BULLETIN OF
THE BRITISH MUSEUM (NATURAL HISTORY)
GEOLOGY SUPPLEMENT 5

LONDON : 1969

BRITISH AVONIAN (CARBONIFEROUS)
CONODONT FAUNAS, AND THEIR VALUE

IN LOCAL AND
INTERCONTINENTAL CORRELATION

FRANK HAROLD TREVOR RHODES^ RONALD LEYSHON AUSTIN

and EDRIC CHARLES DRUCE

31 Plates; 92 Text- figures

BULLETIN OF

THE BRITISH MUSEUM (NATURAL HISTORY)

GEOLOGY SUPPLEMENT 5

LONDON : 1969

THE BULLETIN OF THE BRITISH MUSEUM

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Bull. Br. Mus. nat. Hist. (Geol.)

Trustees of the British Museum (Natural History) 1969

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BRITISH MUSEUM (NATURAL HISTORY)

Issued 21 February 1969 Price £11

BRITISH AVONIAN (CARBONIFEROUS)
CONODONT FAUNAS, AND THEIR

VALUE IN LOCAL AND
INTERCONTINENTAL CORRELATION

By F. H. T. RHODES, R. L. AUSTIN & E. C. DRUCE

I.
II.

III.

IV.

VI.

VII.

VIII.

IX.

XI.

CONTENTS

Purpose and scope of present study .

History of previous research ....

(a) Conodont research in Britain ....

(b) Carboniferous conodont zonation and correlation
Stratigraphy .......

(a) Introduction to the stratigraphy of the Carboniferous of

Britain

(b) The Avonian succession

the Carboniferous of Europe

(d) The stratigraphy of areas from which conodonts are

described ....
(i) The Avon Gorge, Bristol
(ii) South Wales
(iii) Shropshire
(iv) Yorkshire
(v) Scotland
Methods of study
Conodont faunas

(a) General Review

(b) Stratigraphical distribution of conodont faunas

(d) Intra-Avonian correlation in Britain

(i) Avon Gorge — North Crop
(ii) Farlow .....
(iii) Yorkshire .....
(iv) Scotland ......

(e) Correlation of the Avonian with Europe and North America
Systematic palaeontology .
Summary and conclusions .
Acknowledgments
References .....
Appendix .....

(a) Sample Register .

(b) Register of Figured Specimens
Index ......

Page
4
5
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7
ii

22
25
25

29
3i
3i
3i
32
35
4 6
46

48
48

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278

279
292
292
293
305

BRITISH AVONIAN CONODONT FAUNAS

ABSTRACT

The conodont faunas of the Lower Carboniferous of the South West Province, the
Yoredales and the Midland Valley of Scotland are described. A complete series of
samples was collected from the Avon Gorge section, Bristol, and also from composite
sections from the North Crop of the South Wales Coalfield, the Clee Hills, Wensley-
dale, Dunbar, Fife, Roxburgh, Midlothian, Ayrshire and Argyll. A total of over
600 samples was collected at intervals ranging from ten feet (Avon Gorge) to six
inches (Dunbar). The calcareous samples were dissolved in either 8% acetic acid or
15% formic acid, and the argillaceous samples subjected to 100 vol. hydrogen
peroxide. Some 3 tons of rock was processed.

All collected sections are illustrated and charts of the conodont abundance (number
of specimens per kilog.) and weight of rock dissolved, together with sample numbers,
are presented. In all, the samples yielded over 25,000 identifiable specimens,
referable to 167 species, belonging to 29 genera, of which 2 named genera (Clydag-
nathus and Patrognathus) , 40 species and 13 subspecies are new. All species are
described and illustrated, and range charts of their vertical distribution are pre-
sented.

The faunas are divided into a total of 14 conodont assemblage zones and correla-
tions are made between standard sections in the various Carboniferous provinces of
Great Britain. There is a strong general similarity between the succession of
conodont faunas in North America, Germany and Britain, although there are also
some striking local differences. These are analysed in the light of conodont phylo-
geny, distribution, and of possible sedimentary breaks in various sections. Correla-
tions are made with the standard goniatite sections of Germany and with the type
sections of the Mississippi Valley.

Within the South West Province the basal part of the K Zone is correlated with the
Cu I goniatite zone and the upper part with Cu II a ; the uppermost K to the Upper
S2 Subzone is correlated with the Cu II Zone, and the D 1( D2, and D 3 Subzones with
the Cu III goniatite zone.

The upper part of the Calciferous Sandstone Measures of the Midland Valley of
Scotland is of Cu III a age, the Lower Limestone Group is of Cu III (3-y age, and the
Upper Limestone Group is of E1-E2 (Namurian) age.

I. PURPOSE AND SCOPE OF PRESENT STUDY

Conodonts were first described in 1856, and, although they were described in only
a few papers in the subsequent seventy-five years, there is now a total of some 1,200
publications devoted to them. Doubt and controversy concerning their function
and affinities remain greater now than a century ago. One recent author (Fahlbusch,
1964 ; see also Beckmann et at., 1965) has argued that they represent algae, and
another that they were internal supports in some ciliated tentacle apparatus of an
unknown filter-feeding organism (Lindstrom, 1964), while still another (Foss, i960)
has suggested that the similarity of their carbonate fluorapatite composition to that
of scales of the Ordovician chordate Astraspis implies an affinity between the two.

BRITISH AVONIAN CONODONT FAUNAS 5

Studies of amino acid content and of ultramicroscopic structure of conodonts at
present in progress may provide important new information on their affinities
(Schwab, 1966 ; Armstrong & Tarlo, 1966).

In spite of the uncertainty concerning their nature and function, studies on cono-
dont successions during the last decade have shown conodonts to be one of the most
sensitive and useful fossil groups available for stratigraphic correlation. Recent
work by German palaeontologists (see p. 8 for detailed references) on the conodont
faunas of the type sections of the Upper Devonian and Lower Carboniferous has
provided the means of making even more precise regional correlation than those
recognized by goniatites upon which " standard " correlations have been established
(see, for example, Ziegler 1962). Furthermore, a broadly similar zonal sequence of
conodonts has been established in the Mississippi Valley.

The purpose of the present paper is to describe conodont faunas from the
" Lower " Carboniferous rocks of the type section in the Avon Gorge, Bristol, from
various parts of South Wales, and from Shropshire, Yorkshire and Scotland. Over
600 samples from these areas have been processed, and have yielded over 25,000
identifiable specimens. The sequence of the conodont faunas at present described
provides the basis for a conodont zonation, which not only assists intra- and inter-
basinal correlation in Britain, but also allows the first precise correlation with North
America and Continental Europe.

II. HISTORY OF PREVIOUS RESEARCH
(a) History of previous conodont research in Britain

Conodonts were first described by Pander (1856) and, although they were reported
shortly afterwards from several localities in Britain, comparatively little attention
has been paid to them in this country.

Walliser (1958) recorded the oldest known stratigraphic occurrence in Britain,
when he discovered a " paraconodont " from the Upper Cambrian Comley Limestone
of Shropshire.

Ordovician conodont faunas from Britain have been described from the Arenigian
of the Southern Uplands (Smith 1907 ; Lamont & Lindstrom 1957) ; the Llan-
deilian Llandeilo Limestone of Carmarthenshire (Rhodes 1953), and Castell Lime-
stone of Pembrokeshire (Bergstrom 1964) ; the Upper Llandeilian and Lower
Caradocian of the Southern Uplands ; the Caradocian wilsoni Shales of the Southern
Uplands (Lindstrom 1957), Gelligrin, Pen-y-garnedd, Crug and Bryn Pig Limestones
of Wales (Rhodes 1953 : Lindstrom 1959 : Bergstrom 1964) and the Ashgillian
Keisley Limestone of Westmorland (Rhodes 1955) and Birdshill Limestone of
Carmarthenshire (Bergstrom 1964).

A number of early workers, including Harley (1861), Moore (1864), Young (1880A)
and Smith & Jones (1881), recorded conodonts from Silurian rocks in Britain.

A basal Llandovery fauna referable to the celloni Zone of Walliser (1964) from the
Malverns was described by Brooks & Druce (1965). Llandoverian conodonts have
also been noted by Whittard (1927) from the Pentamerus Beds of Shropshire and by
Squirrell & Tucker (i960) from the Upper Llandoverian of the Woolhope Inlier.

6 BRITISH AYONIAN CONODONT FAUNAS

WenLockian conodonts have been collected from the Welsh Borderland by Hill (1936)
and systematically described from Usk by Austin & Bassett (1967). Conodonts
from the Woolhope, Wenlock, Aymestry and Whitclifhan Limestones of the Welsh
Borderland were reported by Ireland (1958, 1962). Rhodes (1953) with Newall
(1963) systematically described a fauna from the Aymestry Limestone of Shropshire
and South Staffordshire. Squirrell & Tucker (i960) listed Upper Ludlovian cono-
donts from the Woolhope Inlier and Collinson & Druce (1966) systematically
described a fauna from the Whitcliffe Flags of Shropshire which was referable to the
eosteinhomensis Zone of Walliser (1964).

Dineley & Rhodes (1956) described Devonian conodonts from the Upper Givetian
at Torquay, from the Lower Frasnian near Chudleigh, from the Lower Frasnian at
East Ogwell and from the Lower Pilton Beds (Strunian) at Saunton, North Devon.
They also described (1957) an Upper Devonian fauna from the limestones of the
Bishopsteignton borehole. Matthews (1962) reported a late Eifelian fauna from a
Middle Devonian limestone at Neal Point in the Tamar Valley. House (1963, table
2) and House & Selwood (1964) have summarised known Devonian conodont
occurrences in South West England. The only new conodont record noted by House
& Selwood was an Upper Givetian conodont fauna from the Marble Cliff Beds,
identified by Rhodes. Rhodes also identified Lower Givetian conodonts from the
Middle Gramscatho Limestones for Hendriks (1966). Other limestones yielding
Siegenian, Emsian and Middle Devonian conodonts are also mentioned. Ziegler
(Hendriks 1966) has also extracted Frasnian conodonts from limestones interstitial
with the Mullion Island pillow lavas.

British Lower Carboniferous conodont studies have been few and brief. Moore
(1863, 1870) listed conodonts from the Carboniferous Limestone of Yorkshire and
Cumberland, Fowler (1955) mentioned conodonts obtained from a borehole in South-
East County Tyrone, Eire, and Robbie (1955) reported conodonts from the Rossmore
and Edenbrook beds of Lower Carboniferous age obtained from the subsurface at
Edenork, County Tyrone, Ireland. Dineley & Rhodes (1956) studied eight samples
from the Tournaisian of South West England. Small faunas from the Shirehampton
Beds, the Lower Limestone Shale, the Black Rock Limestone, the Fish Bed and
Horizon y, collected in the Avon Gorge, Bristol, were described, as also were faunas
from the ? Black Rock Limestones of Windsor Hill, Somerset and Waterlip Quarry,
Somerset. Matthews (1961, 1966) has identified anchoralis faunas collected at
Viverdon Down near Callington, and from the St. Mellion area of South West
England. Varker (1967) has described conodonts referable to the genus Apatog-
nathus from the Yoredales of Northern England.

Young (1880, 1880A) mentioned the occurrence of Scottish Carboniferous Lime-
stone conodonts, in addition to those of the Silurian and Devonian of England.
Smith (1900) reported conodonts from the Carboniferous limestones of Western
Scotland and figured those described by Hinde (1879, 1900). These were sub-
sequently refigured and redescribed by Clarke (i960) who also described faunas from
the Scottish Carboniferous Limestone Series. Craig (1952, 1954) reported conodonts
from the Top Hosie Shale, of Lower Carboniferous age, near Kilsyth, Scotland.

BRITISH AVONIAN CONODONT FAUNAS 7

Namurian conodonts were found in a borehole in a Yoredale type of deposit in the
Cleveland Hills by Fowler (1944). Dunham & Stubblefield (1945) noted the
occurrence of a platform conodont in the Colsterdale Marine Beds of the Millstone
Grit of Yorkshire. Conodonts have also been noted in the Millstone Grit of the
Midlands by Stevenson & Mitchell (1955). The only published systematic des-
cription of British Namurian conodonts is that by Higgins (1961) who described a
fauna from the Namurian of North Staffordshire. Collinson & Druce {in press) have
described a conodont fauna from the lower boundary of the Namurian in County
Clare, Eire.

There have been no detailed systematic descriptions of British Pennsylvanian
conodonts, but many workers have noted the presence of conodonts in the British
Coal Measures. In Scotland, Currie, Duncan & Muir-Wood (1937) described
conodonts from Skipsey's Marine Band, and the Upper Coal Measures in Central and
West Scotland. Manson (1957) listed conodonts from a marine band in the Anthra-
conaia modiolaris Zone of Scotland. Smith (1907A) recorded conodonts from the
Upper Coal Measures (above the Craigmore Ironstone).

Stevenson & Mitchell (1955), Stubblefield & Calver (1955), Mitchell (1954) and
Eden (1954) reported conodonts from the Midland Coalfields, as also have Mitchell &
Stubblefield (1941) from the Leicestershire and South Derbyshire Coalfield, Mitchell,
Stubblefield & Crookall (1942, 1945) from the Warwickshire and northern part of the
South Staffordshire Coalfields, Edwards & Stubblefield (1948) from the Derbyshire
and Nottinghamshire Coalfields, and Edwards (1954) from the Clown Marine Band
in Derbyshire and Nottinghamshire. Earp & Magraw (1955) listed conodonts from
the Tonge's Marine Band in the Lower Coal Measures of Lancashire, and Magraw
(1957) recorded conodonts from various marine bands in Lancashire, Derbyshire and
Yorkshire. Ramsbottom (1952) and Woodland, Archer, Evans & Calver (1957)
noted the presence of conodonts in the South Wales Coal Measures.

There has been no reference to the occurrence of post-Pennsylvanian conodonts in
the British Isles.

(b) Carboniferous conodont zonation and correlation

Although the Upper Devonian and Lower Carboniferous rocks of West Germany,
the latter of which provide the standard for Carboniferous correlation, are tradi-
tionally correlated on the basis of their cephalopod faunas, recent studies by German
palaeontologists on the conodont faunas have shown that the latter offer a new
degree of precision in problems of regional correlation. The most notable contribu-
tions in this field are those of Bischoff (1955, 1956, 1957), Bischoff & Ziegler (1956,
1957), Bartenstein & Bischoff (1962), Boger (1962), Kronberg, Pilger, Scherp &
Ziegler (i960), Meischner (1962), Sannemann (1955, 1955A), Voges (1959, i960),
Walliser (1958, i960) and Ziegler (1958, 1959, 1962, 1962A, 1962B). These workers
described conodonts, which were associated with the classic Devonian and Lower
Carboniferous cephalopod zones in West Germany, and a detailed Devonian and
Lower Carboniferous conodont faunal succession has thus been established.

8 BRITISH AVONIAN CONODONT FAUNAS

This conodont succession has been applied to rocks of Upper Devonian and
Carboniferous age in other parts of Western Europe, notably by Dvorak & Freyer
(1961), Helms (1959, 1961), and Muller (1959) in East Germany ; Flugel & Ziegler
(1957) in Austria ; Lys & Serre (1958), Higgins (1962), Higgins, Wagner-Gentis &
Wagner (1964) in Spain ; Lys & Serre (1957), Lys, Serre & Deroo (1957), Lys, Serre,
Mauvier & Grekoff (1961) in France and the Sahara ; Boogaard (1963) in Portugal ;
and by Serre & Lys (i960) and Conil, Lys & Mauvier (1964) in Belgium.

Germany

The zonation of the Lower Carboniferous in Germany is based chiefly on the work
of Bischoff (1957) and Voges (1959).

Bischoff (1957) studied the conodont faunas of the Wocklumeria, Gattendorfia,
Pericyclus and Goniatites Stages of the Rhenoherzynicum. He subdivided the
Pericychis Stage into two conodont subzones — the Siphonodella Subzone (Cull a-(3)
and the anchor alis Subzone (Cull y). He also described the conodont faunas of the
three goniatite zones of the Goniatites Stage.

Voges (1959) described conodonts from the Lower Carboniferous Gattendorfia and
Pericyclus Stages. He recognized three zones within the Gattendorfia Stage : the
Gnathodus kockeli-Pseudopolygnathus dentilineatus Zone ; the Siphonodella-
Pseudopolygnathus triangulus inaequalis Zone and the Siphonodella-Pseudopoly-
gnathus triangulus triangulus Zone. Three zones were recognized by Voges within
the Pericyclus Stage ; the Siphonodella crenulata Zone (Cull a), which was sub-
divided into a lower and an upper subzone, the Scaliognathus anchoralis Zone (Cu
II Py), and a Scaliognathus anchor alis-Gnathodus bilineatus " interregnum " (Cu
II S). Voges thus gave a more detailed and refined zonation than Bischoff (1957)
for the Gattendorfia and Pericyclus Stages, and also differed from Bischoff by extend-
ing the Scaliognathus anchoralis Zone into Cu II (5 (Bischoff confined the anchoralis
Zone to Cu II y).

The German workers were thus the first to attempt a conodont zonation of the
Lower Carboniferous. Whilst not detracting in the least from the excellent work of
Bischoff and of Voges it is true to say that there are a number of deficiencies and gaps
in our knowledge of German conodont faunas. The reasons for these gaps are twofold.
Firstly the nature of the outcrops is such that it is impossible to collect from con-
tinuous exposures. The different samples collected by both Voges and Bischoff are
from widely separated areas. Secondly, the sediments are such that in any one
locality not all horizons yield conodonts (e.g. Hangenberg Schiefer, and the cherts
immediately beneath the " Erdbach Kalk "). There has also been a marked
tendency for German conodont workers to give total stratigraphic ranges of species,
rather than the exact distribution and abundance of individual species, although
more recently, for example Kronberg, Pilger, Scherp & Ziegler (i960) and Ziegler
(1963), these have been given. It is becoming increasingly apparent from conodont
studies in other parts of the world that numbers of stratigraphic breaks exist in the
German succession, even where these have not hitherto been suspected.

BRITISH AVONIAN CONODONT FAUNAS 9

The Franco-Belgian Province

Studies of the Franco-Belgian Lower Carboniferous conodont faunas are com-
paratively recent. Serre & Lys (i960) described the distribution of Tournaisian and
Visean conodonts in the Avesnois, Boulonnais and Hainault regions of Northern
France and Belgium, and Conil, Lys & Mauvier (1964) recorded the ranges of conodont
species in the type formations of the Dinantian in the Franco-Belgian Province.
More recently Bouckaert & Ziegler (1965) have published an account of the conodont
faunas of the Famennian Stage in Belgium.

Conodont studies in the Franco-Belgian Province are important because these
sections have yielded the type specimens of many Lower Carboniferous cephalopods.
Unfortunately, however, neither Serre & Lys nor Conil, Lys & Mauvier have system-
atically described or illustrated their specimens, and they have given no exact
distribution or abundance data for individual species. Thus the work at present is
of limited value. Few correlations can be made, although one which can be made
with a fair degree of certainty is based on the distribution of Scaliognathus anchor alis.
This species is restricted to Tn3 b in the Franco-Belgian Province and to the Cu
II p y horizon in Germany. This is important, because hitherto it has been con-
sidered likely that the Tournaisian- Visean boundary in Germany should be drawn
at the base of Cu II (3 y, based on the distribution of Pericyclus princeps. This is the
zonal fossil for Cu II a in Germany and was first found and described from the Tn 3c
of Belgium. If the conodont correlations based on anchor alis are accepted, they are
at variance with the " well established " goniatite evidence, although the literature
does not contain a single reference to Pericyclus princeps having ever been found in
Germany. It is therefore a very dubious " zonal fossil ".

The need for systematic descriptions and illustrations of the Franco-Belgian
conodonts is thus urgent for it may provide the key for unravelling the German
succession and for filling the gaps which are present in Germany.

The United States

Lower Carboniferous conodont research in North America began in the mid
nineteen-thirties. Huddle (1934) described the conodont fauna of the New Albany
Shale in Indiana and Branson & Mehl, working in Missouri, described the conodont
faunas of the Bushberg Sandstone (1934A), of the "Lower Mississippian Formations"
(1938A), of the Caney Formation (1940) and of the Keokuk Formation in Iowa and
Missouri (1941A). E. R. Branson (1934) also described conodonts from the Hannibal
Formation in Missouri.

Cooper (1939) described conodonts from the Bushberg Hannibal strata in Okla-
homa and later, with Sloss (1943), described a fauna from a Lower Mississippian
black shale in Montana and Alberta.

Mehl & Thomas (1947) described the conodont fauna of the Fern Glen Formation
in Missouri, and Thomas (1949) described the faunas of Lower Mississippian age from
the English River and Prospect Hill Siltstones of South East Iowa.

Hass described Lower Carboniferous conodonts from the Arkansas Novaculite of

io BRITISH AVONIAN CONODONT FAUNAS

Arkansas (1956A), the Maury Shale of Tennessee (1956), the Barnett Formation
(1953) and the Chappel Limestone of Texas (1959).

Scott & Collinson (1961) described a fauna from the Louisiana Limestone and
from the McCraney Limestone.

Youngquist & Patterson (1949) described conodonts from the Prospect Hill Sand-
stone of Iowa. The fauna of the Lower Mississippian Wassonville Dolomite of Iowa
was described by Youngquist & Downs (1951). Youngquist, Miller & Downs (1950)
described Burlington conodonts from Iowa.

Rexroad (1957) described Chester conodonts from Illinois and later (1958) from the
Glen Dean Formation. Rexroad & Clarke (i960) described Glen Dean conodonts
from Kentucky, Virginia and West Virginia. Golconda Group conodonts were
described by Rexroad & Jarrell (1961). Those of the Kinkaid Formation in Illinois
were described by Rexroad & Burton (1961) and those of the Paoli and equivalent
formations in Illinois by Rexroad & Liebe (1962).

From the work of these and other workers, it became clear that conodonts were
abundant in Mississippian rocks and were useful for correlation of strata. As a
result, the Illinois State Geological Survey, in co-operation with the University of
Texas, the State University of Iowa, Texas Technological College, the University of
Houston, and the Indiana Geological Survey, conducted a programme of research in
the Mississippi Valley. In 1962 Collinson, Scott & Rexroad published a paper in
which they described 17 conodont biostratigraphic zones, which were present in the
Mississippian rocks of the Mississippi Valley. The limits and characteristic species
of each zone were described and they also attempted to correlate these zones with the
conodont zones present in Germany.

Subsequent workers have systematically described the faunas of the biostrati-
graphic zones established in 1962. Thus Rexroad & Collinson (1963) not only
described the conodonts of the St. Louis Formation, but also indicated, described
and illustrated the species characteristic of the Taphrognathus varians-Apatognathus
Assemblage Zone and of the Apatognathus ? geminus-Cavusgnathus Assemblage Zone.

In the same way Rexroad & Scott (1964) when describing the conodont faunas of
the Rockford Limestone and the lower part of the New Providence Shale of Indiana
described and illustrated the conodont fauna characteristic of the Siphonodella
isosticha-S. cooperi, Gnathodus semiglaber-Pseudopolygnathus multistriatus, Bactro-
gnathus-Polygnathus communis and Bactrognathus-T aphrognathus Assemblage Zones.
They also showed in tables the numerical distribution and stratigraphic ranges of
specimens.

Rexroad & Collinson (1965) provided the same data for the Taphrognathus varians-
Apatognathus Assemblage Zone, when describing the conodonts of the Keokuk,
Warsaw and Salem Formations of Illinois.

Rexroad & Furnish (1964) referred their fauna from the Pella Formation of South-
Central Iowa to the Gnathodus bilineatus-Cavusgnathus charactus Assemblage Zone of
the Mississippi Valley, and to the St. Genevieve Limestone in particular.

Rexroad & Nicoll (1965) described the faunas of the Menard Formation, which
they referred to the Kladognathus-Cavusgnathus naviculus Zone, drawing the lower

BRITISH AVONIAN CONODONT FAUNAS n

limit of that zone at the base of the Menard. Klapper (1966) described Upper
Devonian and Lower Mississippian faunas from Montana, Wyoming and South
Dakota, and identified the local equivalents of the German Cu I and Cu II a faunas.
These studies have provided a most useful basis for the correlation of our Avonian
faunas with those of the Mississippi Valley.

Australia

Recent studies by Glenister & Crespin (1959), Glenister (i960), Jones & Druce
(1966) and Glenister & Klapper (1966) have shown the similarity of European-
North American Devonian and Lower Carboniferous conodont faunas to those of
comparable age in Australia.

III. STRATIGRAPHY

(a) Introduction to the stratigraphy of the Carboniferous of Britain

Rocks of Lower Carboniferous age form one of the most extensive outcrop belts in
the geology of Britain but, in spite of their extensive outcrop, generally good expo-
sure, and the wealth of study devoted to them, precise correlation is often difficult
between basins, and sometimes also within them. The distribution and character
of Lower Carboniferous rocks is so well known that it needs only the merest introduc-
tion in a study such as this, as it has recently been reviewed by George (1958).

Lower Carboniferous rocks were deposited on an archipelago-like basement (Fig.
1) dominated by a landmass to the north-west, by a caledonoid-trending massif
which extended from north-eastern Ireland into the Southern Uplands, by a stable
block in north-eastern England, and a great, east-west landmass, stretching from
Leinster through Central Wales into the Midlands of England. To the south of this
landmass, the south-western Province of the Carboniferous represented a basin of
more or less continuous deposition, which extended westwards into Ireland and was
bounded by a landmass in south-western Cornwall. It was marked by the deposi-
tion of two distinctive facies groups. In the south, the Culm facies of Devon and
Cornwall and southern Ireland included dark argillaceous and sometimes calcareous
shales and mudstones, containing a few thin, impure, dark limestones and cherts, as
well as subordinate sandstones and grits. To the north of this facies, in Somerset,
Gloucestershire and South Wales, there was deposited the " limestone facies,"
consisting mainly of grey or light-blue bioclastic limestones, with subordinate
dolomites, oolites and argillaceous limestones. These rocks contain a rich fauna of
brachiopods and corals, as well as crinoids, ostracods, foraminifera and algae. In
some parts of the section there is developed a " lagoon " facies, characterized by
drab grey, calcite-mudstones, with subordinate calcareous shales and oolitic rocks.
Calcareous algae, ostracods, gastropods and pelecypods are the main fossils of this
group, which is present in the Modiola phase of south-western England. Both the
Culm facies and the bioclastic limestone facies extend westwards into southern
Ireland.

Northern England was separated from Southern England for at least part of
Carboniferous times, by the combined St. George's Land-Midland Barrier. In the

BRITISH AVONIAN CONODONT FAUNAS

Fig. i. Generalized palaeogeographic map of Britain during Early Carboniferous times,
showing main depositional regimes, and localities described in the text. Based partly
on George (1958) and Wills (1952).

BRITISH AVONIAN CONODONT FAUNAS 13

Central Province, lying to the north of this barrier, rocks of Yoredale facies were
deposited. These include cyclothemic limestones, non-marine sandstones, shale, and
coal sequences, with a fauna of corals, brachiopods, bivalves, occasional goniatites
and non-marine plants. Bioclastic limestones and spectacular reefs also developed
in various places in this region, such as the reef knolls of Derbyshire and the Craven
Lowlands, and the larger sheet-like apron reefs of Southern Ireland.

In the Northumbrian trough, lying to the north of the Central Province, as well as
in the trough of the Midland Valley of Scotland, which was separated from it, a
distinctive facies of the Cementstone type was developed, consisting of alternating
thin argillaceous limestones, sandstones and grey-black shales. Fossils are rare and
include fish, ostracods, inarticulate brachiopods and spirorbid worms. These rocks
are overlain by sandstones, coal-bearing strata and limestones, the total Northum-
brian section including some 7,000 ft. of strata. In the Midland Valley of Scotland,
a broadly similar variety of rock types is found, although there is no detailed
equivalence in age ; clastic deposits predominate there, and include the Oil Shales
and the Calciferous Sandstones. There are also thick lavas in places.

In north-western Ireland great thicknesses of deltaic strata were deposited, which
pass southwards into limestone-shale and bioclastic limestones (George 1955).

Rocks of Lower Carboniferous age present formidable problems of correlation and
these arise largely from the rapid and almost continuous lithological and faunal
changes which they display. The general problems of correlation have been
reviewed by Rayner (1953) and by George (1952 and 1958). The first successful
attempt to provide a palaeontological subdivision of the rocks of the South-West
Province was that of Vaughan (1905) who proposed the now widely-applied coral-
brachiopod system for the limestones of south western England. This was based
upon exhaustive and meticulous collecting of faunas, especially from the Avon Gorge.
Vaughan established his zonal scheme on the first appearance of particular genera
and species, although the zones as interpreted today are partly assemblage zones,
based on the occurrence of a number of species. To a varying extent the demarca-
tion of Vaughan 's zones was influenced by the marked lithological changes which
occur in the Avonian strata of south-western England (see p. 17).

It was early recognized that Vaughan's zonal scheme was inapplicable to the
different facies of northern England and in that area the work of Bisat (1924) on
goniatites provided the basis for much of the present classification.

Present views on the validity of these various zonal schemes are sharply divided.
There is general agreement that, in the sense in which they were originally established
by Vaughan, the coral-brachiopod zones can no longer be applied in detail, but some
workers, especially Kellaway & Welch (1955), reject the whole zonal scheme which
they represent. The detailed problems of correlation are discussed on p. 52.

(b) The Avonian Succession

The Avon Gorge, Bristol, has long been regarded as the type area for the British
" Lower " Carboniferous. The base of the Lower Limestone Shale was selected by
Buckland & Conybeare (1824) and by De la Beche (1846) as the base of the Lower

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Carboniferous. Although Vaughan (1905) established a series of coral-brachiopod
zones for the succession, these were later found to be of only local value in correlation
(see George 1952, 1958 for a critical review), so that other type sections have been
recognized for other areas of Britain (e.g. Walker 1964). The accepted international
type section for the Lower Carboniferous is that in West Germany.

The rocks of the Avon Gorge comprise some 3,000 ft. of strata, consisting pre-
dominantly of carbonates, but with subordinate shales and sandstones. Vaughan
(1905) subdivided these into five faunal zones, four of which were divided into two
subzones (Fig. 2). Vaughan pointed out that the Dinantian was approximately, but
not exactly, equivalent to his Avonian, which he subdivided into the underlying
Clevedonian (C, Z, K) and the Kidwellian (D and S Zones), rather than using the
equivalent Tournaisian and Visean. Vaughan modified his classification in later
publications (1906, 1915 : Dixon & Vaughan 1911, Reynolds & Vaughan 1911).
The modifications involved the inclusion of the Modiola phase as the basal subzone
of K (Km), the varying position of horizon y (included in Z in 1905 ; in C in 191 1 ;
included as the major part of C in Burrington Combe in 1911), and the development
of the Caninia Zone (1906, 1911). Other authors also proposed subsequent amend-
ments, Dixey & Sibly (1918) subdividing the C Zone in South Wales, and Hudson &
Dunnington (1945) placing the Caninia Oolite in the Upper C Zone.

The present standard coral-brachiopod zonation of the Avonian (modified after
George 1958) is as follows :

6 DlBUNOPHYLLUM ZONE

5 Seminula Zone

4 Upper Caninia Zone

3 Lower Caninia Zone
2 Zaphrentis Zone
1 Cleistopora Zone

Symbols
D

C 2 S

201

Vaughan (1905) Subzones

D2 and Di.

Vaughan (1905) " Main

Seminula Zone " of Dixey

& Sibly (1918).

Dixey & Sibly (1918).

This includes part of Vau-

ghan's (1905) Syringothyris

Zone and the overlying

Lower Seminula Zone (Si).

The lower limit of this zone

is placed at the top of the

Caninia Oolite.

Dixey & Sibly (1918), with

horizon y at the base.

Vaughan (1905) Subzones

Z2 and Z,\.

M and K Zones of Vaughan

(1905) and the K Zone of

Sibly (1906).

BRITISH AVONIAN CONODONT FAUNAS

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BRITISH AVONIAN CONODONT FAUNAS 17

In this succession, Zones 1-3 are generally regarded as Tournaisian, and Zones
4-6 as Visean.

Vaughan's general zonal scheme has been the subject of much subsequent criticism,
partly because of the extent to which the distribution of corals and brachiopods is
influenced by environment, and partly also because of the lack of precision in
defining boundaries. The K Zone, for example, was coincident with the lithological
limits of the Lower Limestone Shale, its only fossil of any possible diagnostic value
being Avonia bassus (George 1952). The faunas of other zones were no less reflec-
tions of the facies changes represented by successive strata, the zaphrentid corals
being but one example. In other areas, zonal fossil genera were found beyond the
limits of these zones.

It was for these reasons that Kellaway & Welch (1955) suggested the replacement
of Vaughan's zones by a succession of lithological units (Fig. 3). The object of these
was to assist in regional mapping, but such lithological units are of less value in
correlation than Vaughan's imperfect faunal zones. Even Kellaway & Welch,
whose divisions generally correspond with the limits of Vaughan's faunal zones,
found lateral transition within this area, the Shirehampton Beds of Bristol passing
southwards into the base of the Lower Limestone Shale, and northwards and
westwards into the top of the Portishead Beds.

Vaughan's faunal assemblage zones, defined by twin zonal indices, but strength-
ened and supplemented by other index fossils, still seem to us to represent the most
satisfactory method of correlation in the field, although we believe that the conodont
zonation presented in the present paper provides a far more precise alternative for
those strata in which conodonts are present.

The correlation of the British Avonian with the continental succession has
presented acute problems. Vaughan (1915) attempted to use the coral-brachiopod
faunas to correlate with the Belgian succession. He correlated the Lower Tour-
naisian (Ti) with his Z Zone and the Upper Tournaisian (T 2 ) with his C Zone
(including the y horizon), making detailed correlations within the various units. He
suggested that the faunal overlap (the Sublaevis Beds and the Marbre Noir Series)
between the Visean and Tournaisian in the Dinantian succession was equivalent to
the Upper C2 and Si Zones, and the Visean succession above V ia up to and including
V 2cx to the S Zone. He correlated the Lower V 2c Beds with the Di, and the Upper
V 2c with the D 2 of the Avon Gorge. Vaughan correlated the Hastiere Limestone
and Shale, the " Octoplicata " Shale, and the base of the Landelies Limestone with
his (3 horizon, but Paul (1937), on the basis of brachiopod faunas, suggested the
equivalence of the upper part of Ki and of K 2 in the Avon Gorge with the Hastiere
Limestone (Tn lb ). He regarded the Hastiere Limestone and the Per acuta Shale
(Tn 2a ) as equivalent to the Gattendorfia Hangenberg Limestone of Germany, but
Goldring (1958) suggested from their trilobite faunas that both these formations may
be equivalent to the Lower Limestone Shale (Ki and K 2 ), and he correlated the base
of the Black Rock Limestone (Zi) with the base of the Landelies Limestone (Tn 2b ).

18 BRITISH AVONIAN CONODONT FAUNAS

The outstanding difficulty of detailed correlation of the Avonian with the Car-
boniferous type sections of the Rheinisches Schiefergebirge has been the absence of
goniatites in the type Avonian section. A prolecanitid (Protocanites) (identified by
Professor Frank Hodson) from shales near Abergavenny may have been collected
from the lithologically similar shales at the top of the Z Zone or from the K Zone.
The exact locality is not specified on the specimen, which is in the Geological Survey
Collections (No. G.S.M. 82817) (see also George 1952 : 35). George & Howell (1939)
have described Prolecanites discoides, Muensteroceras inconstans, and Pericyclus kochi
from the Upper Caninia Oolite of Three Cliffs Bay, Gower, and these suggest an
uppermost Tournaisian age for these beds, while the presence of Muensteroceras
euryomphalus and Merocanites cf. compressus in the overlying Upper Caninia Beds
suggest a low Visean age (George & Ponsford, 1935). The traditional Lower-Upper
Avonian boundary (Dixon & Vaughan, 1912) of the Lower Caninia Zone (Ci) and
Upper Caninia Zone (C2S1) is thus approximately equivalent to that of the Tour-
naisian and Vis6an (see George 1952, 1955). Smith (1942 : 338) recorded a goniatite
indicative of a P2 age from the Avonian Tanhouse Beds (D 3 ) of the Yate district in
Gloucestershire.

Currie (1954) provided a monographic study of Scottish Carboniferous goniatites
which allowed her to make correlations with the stages established by Bisat. She
was able to assign the Upper Limestone Group to the E2 (Arnsbergian) Stage, the
Limestone Coal Group to the Ei (Pendleian), both the latter being of Lower
Namurian age, the Lower Limestone Group to the P2 and the Upper and higher part
of the Lower Oil Shale Group of the Calciferous Sandstone 'Series' to the Pi and B
Stages (Bollandian and Cracoean) of the Middle and Upper Visean. Bisat's B2, Pi
and P2 goniatite zones are equivalent to Vaughan's Dibunophyllum Zone, and his
Bi Zone to the main Seminula Zone. Prentice & Thomas (1965 : 43, Fig. 2) have
given a distribution table of British prolecanitids in which they show a correlation of
Vaughan's D-C Zones in North Devon with the European goniatite zones, although
they provide no detailed discussion of the broader aspects of correlation.

In spite of these various studies, Lower Carboniferous correlations between Britain
and continental Europe remain tenuous, the uncertainties arising chiefly from the
absence of the more stratigraphically useful faunal groups common to the two areas.
We believe that the closely comparable conodont faunas here described allow a far
more refined correlation than any yet achieved.

(d) The stratigraphy of areas from which conodonts are described
(i). The Avon Gorge, Bristol.

The Avon Gorge, Bristol, is the type area for the British Avonian. A series of
steep, river-side cliffs, provide almost continuous exposures of rocks from the upper-
most Old Red Sandstones at the base, to the highest beds of the D Zone of the
Carboniferous at the top.

The lowest beds of the Avonian section are thinly-bedded, grey, brown, green and
red, marly claystones, thin grits, sandstones and fissile, slightly calcareous shales.
There are few calcareous deposits, the first limestone occurring 12 ft. above the base

BRITISH AVONIAN CONODONT FAUNAS

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20 BRITISH AVONIAN CONODONT FAUNAS

of the section. In the lower portion of the section fossils are rare, ostracods, gastro-
pods and algae being the most common ; brachiopods and bivalves are generally
rare. Ascending the sequence, fine grained compact limestones become more
prominent, their upper bedding surfaces being covered with brachiopods and
crinoids. The upper part of the Lower Cleistopora Beds is an alternating sequence of
claystones and thin limestones, which has a banded appearance. Occasional more
massive limestone bands, about one foot thick, are also interbedded.

The highest beds of the shallow-water phase consist of seven distinct beds,
separated by thin shale partings. The lower six beds range from n inches to z\ feet
in thickness and are crinoidal limestones, which have been stained by haematite.
The uppermost bed (the Bryozoa Bed) is a massive, limestone bed, eight feet thick,
crowded with crinoids, bryozoa and small gastropods.

The Upper Cleistopora Zone consists at the base of sandy fossiliferous limestones
with interbedded calcareous shales. Near the base is a " gritty " six inch bed of
crinoidal limestone, the Palate Bed, which contains bryozoa, palatal teeth and
coprolites. Thinly bedded limestones, and alternating shales follow. The upper-
most beds of the K Zone consist of blue-grey calcarenite beds, up to one and a half
feet thick, and alternating brown silty shales.

Horizon (3 consists of thinly bedded, coarse crinoidal limestone, with thin shale
layers developed between the more massive limestone bands. The beds of the main
Z Zone are blue-grey fossiliferous massive limestones, with some alternating, thinly-
bedded limestones and a few shale partings. The limestones approach a " petit
granit " in character.

The Laminosa Dolomites were probably originally identical to the Z Beds in
lithology, but subsequent dolomitisation has resulted in these beds weathering to a
brownish colour, which contrasts strongly with the blue-grey limestones of the
Zaphrentis Zone beneath and with the white oolites of the Caninia Zone above.

The Caninia Oolite is a pinkish-grey, white-weathering, current-bedded, fine
grained oolite with uniformly rounded grains. It is succeeded by a series of current-
bedded, marly limestones, dolomitic limestones, occasional oolitic bands and blue,
grey, yellow, green or red shales — the Caninia Dolomites and Shales. The uppermost
beds of this group are more massive than the lower and less shale is developed in them.

Shales and thick bands of dolomite with occasional oolites form the lowest beds of
the Seminula Zone. They are essentially similar in lithology to the underlying
Caninia Dolomites. They are followed by massive blue-grey limestones, which are
frequently dolomitised, and by thin shales, which are succeeded in turn by calcite
mudstones, which weather white. The shales become less conspicuous higher in the
section, where grey Lithostrotion-bearing limestones predominate. The upper beds
of the Seminula Zone, the S2 Subzone, consist of oolites and pisolites at the base and
the Concretionary Beds at the top. The latter are fine-grained, argillaceous lime-
stones, the upper surfaces of which are undulating. They are underlain by black
shales, which ramify into the overlying limestone bands. The Concretionary Beds,
which sometimes contain algae and ostracods, are interbedded with chinastones and
occasional oolitic limestones.

BRITISH AVONIAN CONODONT FAUNAS 21

Massive grey foraminifera-bearing limestones, which are oolitic in places, form the
lower beds of the T>i Subzone of the Dibunophyllum Zone. A few pseudobreccias
are also developed. The Upper Di Beds consist of coarse oolites, alternating with
thin shales and grits. In the D2 Subzone the lowest beds show an alternation of
grits, limestones and shales. Higher in the section there are grey oolitic limestones,
which contain foraminifera, crinoids and corals. The highest beds of the section
consist of shales and grits, which are heavily stained with haematite.

The section was sampled at ten-foot intervals, Vaughan's (1906) zonation and
description being used as a basis for the collecting. The section sampled was sub-
divided into nine traverses (Fig. 5). These were as follows : —

1. The riverside traverse of the K Zone. Leigh Woods side of the Gorge. (ST
556 746).

Sample numbers K1-K17.

2. The top of the K Zone and the basal 30' of Zi Quarry 1. Leigh Woods side of
the Gorge. (ST 557 745).

Samples K18-K21 and Z1-Z10.

3. The Zi Limestone traverse in Black Rock Quarry. Clifton side of the Gorge.
(ST 561 747).

Sample numbers Z11-Z20.

74-

Press Qi

CLIFTON DOWN

O 30

3 YARDS

SCALE

Leigh Woods

KEY

Railway

Road -i—ar^:

Traverse No. (5)

ty Rd

/do)

Clifton

Suspension
Bridge

Fig. 5. Sketch map of the Avon Gorge, Bristol, showing localities mentioned in the text.

22 BRITISH AVONIAN CONODONT FAUNAS

4. The Z2 Limestone traverse in Quarry 2. Leigh Woods side of the Gorge.
(ST 558 745)-

Sample numbers Z21-Z38.

5. The Laminosa Dolomite traverse in the Railway cutting, Leigh Woods side of
the Gorge, between Quarry 2 and Quarry 3. (ST 559 745).

Sample numbers Ci-Cii.

6. The Laminosa Dolomite and Caninia Oolite traverse in Quarry 3. Leigh
Woods side of the Gorge. (ST 560 744).

Sample numbers C12-C25.

7. The Caninia Dolomite traverse along the roadside on the Clifton side of the
Gorge, between the Caninia Oolite Quarry to the North and the Great Quarry to
the South. (ST 562 746).

Sample numbers C26-C48.

8. The Si and lower S2 traverse in the Great Quarry on the Clifton side of the
Gorge. (ST 563 740).

Sample numbers S1-S30.

9. The S2 and Concretionary Bed riverside traverse, south of Quarry 4. Leigh
Woods side of the Gorge. (ST 562 737).

Sample numbers S31-S72.

10. The D Zone traverse at the roadside, north of and a short distance to the
south of Bridge Valley Road on the Clifton side of the Gorge. (ST 564 734).
Sample numbers D1-D27.

(ii) South Wales

Rocks of Lower Carboniferous age form an extensive rim around the margins of the
South Wales Coalfield, where they overstep the Old Red Sandstone. The thickest
and most complete sequence is developed on the southern margin of the Coalfield in
Pembrokeshire, Gower and the Vale of Glamorgan. The application of Vaughan's
zonal scheme has shown that in this area the complete succession is present, the total
thickness being in excess of 4,000 ft. in parts of Pembrokeshire and some 3,500 ft. in
Gower, but thinning gradually eastwards. There is a broadly comparable litho-
logical sequence to that of the Bristol area, comprising a lower limestone and shale
sequence, followed by bioclastic limestones and oolites, but including varying
developments of shales and pseudobreccias in the highest parts, and dolomites in the
C and Z Zones in the east. On the North Crop of the coalfield the thickness is much
reduced, however, partly as a result of original depositional thinning against the
margins of a northerly landmass, partly because of intra-Avonian unconformities,
and partly because of truncation below the transgressive unconformable base of the
overlying Millstone Grit. The intra-Avonian unconformity cuts out much of the C
and S Zones in places.

Our collections were made chiefly from the North Crop of the Coalfield, though

BRITISH AVONIAN CONODONT FAUNAS

smaller collections were also made from Gower and Pembrokeshire. Detailed
descriptions of the local stratigraphy have been given by George (1927 and 1954),
Dixey & Sibly (1918) and Owen & Jones (1955). Pringle & George (1961) have
reviewed the regional stratigraphy.

Detailed localities and measured sections are given in Figs 59-92 (p. 246), and
it is necessary here to give only a brief introduction to the local succession. The
youngest strata of the Avonian, the D 3 Upper Dibunophyllum Zone, or Upper
Limestone Shale, are often cut out by Namurian overstep. The succession was
collected by us at Mellte Bridge, at the confluence of the Rivers Mellte and Sychryd,
near Craig-y-Dinas (SN 911079 : see Owen & Jones 1955) where it consists of 23 ft.
of dark shales and interbedded muddy, and rarely crystalline, crinoidal limestones,
most of them less than a foot in thickness. The samples yielded over 3,900 identifi-
able specimens, whereas beds of similar age from the Black Lias Quarry at The
Mumbles, Glamorgan (SS 615883) proved virtually barren in conodonts.

The underlying D2 Beds were first collected from exposures in the valley of the
River Nedd (SN 912122) but these proved to be unfossiliferous, and further collec-
tions were made from Craig-y-Dinas (SN 911099) where some 64 ft. of strata are
exposed. These consist of massive crystalline limestones with thin interbedded
shales. Near the top of the section a thin irregular band of rolled fish framents and
conodonts occurs. The samples yielded over 130 specimens.

ABERGAVENNY

Fig. 6. Map of South Wales to show the main outcrop of the Carboniferous Limestone.

BRITISH AVONIAN CONODONT FAUNAS

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BRITISH AVONIAN CONODONT FAUNAS 25

These beds overlie some 80 ft. of massive crystalline limestones, which are assigned
to the Di Subzone. Near the top a " honeycomb " is developed. These samples
yielded no conodonts, and the underlying 300 ft. of S2 grey crystalline limestone
also proved barren.

The S2 and C2S1 Zones were collected at Llanelli Quarry (SO 223125), the S2
comprising over 300 ft. of dolomitic, sandy, massive bedded limestones with occasional
brachiopod lenses. The C2S1 section consists of about 50 ft. of porcellanous, compact
calcite-mudstones with some oolites and green shales (George 1954). None of the
samples from these exposures yielded conodonts.

The underlying Z Zone was collected at Blackrock (SO 2 13 125) and consists of
190 ft. of alternating oolites and sugary dolomites, with occasional thin shale bands.
All samples in this section yielded conodonts, although some samples yielded only
unidentifiable fragments. Over 5,000 specimens were recovered.

The K Zone was collected in the banks of the River Clydach (SO 224126) and along
the Heads of the Valleys Road (SO 225130), the contacts with the underlying red
sandstone, referred to the Devonian, and the overlying Z Zone both being exposed.
The unit consists of alternating calcarenite and shale bands, which range in thickness
from 40 ft. to six inches. The limestone samples all yielded conodonts but the shales
were unproductive.

(iii) Shropshire

Rocks of Lower Carboniferous age are rare in Shropshire, most of which was
emergent during early Carboniferous times. Strata of Lower Carboniferous age,
which outcrop on the northern and southern flanks of Titterstone Clee Hill, are also
found at Little Wenlock and Lilleshall. Our collections were made at Farlow (SO
642808), on the northern slopes of Titterstone Clee Hill, where conglomerates and
overlying limestones and shales of the K Zone are well exposed. The basal con-
glomerate, which reaches a thickness of some 40 ft. in places (Ball & Dineley 1961),
overlies Grey Farlow Sandstones of the Upper Old Red Sandstone. The K Zone is
overlain by Z Zone oolitic limestones, which are well exposed at Oreton (SO 648806).
The overlying Cornbrook Sandstone, once regarded as representing the Caninia Zone,
has been shown by Jones & Owen (1961) to be of Westphalian age. In contrast, the
youngest Lower Carboniferous strata of the Little Wenlock area represent the
Dibunophyllum Zone.

The Z Zone was collected at Oreton Quarry (SO 648806) where it consists of 20 ft.
of pale cream calcarenite, which yielded abundant conodonts.

The underlying K Zone was collected in Farlow Lane (SO 642808), the contact
between the zones being unexposed. The K Zone consists of alternating shales and
limestones ; the lower shales contain quartz pebbles, and lie directly above con-
glomerates referred to the Old Red Sandstone (Farlovian). Conodonts were
recovered from all samples.

(iv) Yorkshire
The Yoredale Formation (Yoredale Series of Phillips 1836) is a succession of

26 BRITISH AVONIAN CONODONT FAUNAS

cyclothems typically developed in north-eastern England. In the type area on the
Askrigg Block it overlies the Great Scar Limestone and is overlain by the Millstone
Grit. The upper contact is partly conformable, partly unconformable ; the lower
contact is an interdigitation. The typical cyclothem of the Yoredale Formation
comprises a thick marine limestone overlain by shale, which is in turn succeeded
by sandstone (Moore 1958, Walker 1964). The limestones resemble those of the
Great Scar Limestone and the southward failure of the shales and sandstones results
in a diachronous (interdigitating) contact between the Yoredale Formation and the
Great Scar Limestone, obliterating at least three cyclothems. In Northumberland
and Durham the interdigitation occurs at lower and lower levels within the Great
Scar Limestone (here called the Melmerby Scar Limestone). The top of the Yoredale
Formation extends higher than on the Askrigg Block in consequence of the occur-
rence of limestones and the non-occurrence of the typical coarse pebbly sandstones
of the Millstone Grit, in the generally cyclothemic sequence. In terms of the
goniatite zones, the Yoredale Formation varies in age as follows : —

Teesdale early B2 to R lb

Wensleydale (= Yoredale) late B 2 to E lb

Grassington P lc only

The succession in the type area of the Yoredale Formation in Upper Wensleydale
is complex, the major cyclothems between two successive thick limestones often
including minor rhythms, which possess characters of the typical rhythmic unit,
except for the persistence of the limestone (Phillips 1836, Moore 1958, Walker 1964).
The succession (Moore 1958 : 94) is as follows : —

IX Main Limestone
VIII Underset Limestone
VII Three Yard Limestone
VI B
VIA
VI Five Yard Limestone

V A
V Middle Limestone
IV C
IV B
IV A
IV Simonstone Limestone
III C
IIIB
III A
III Hardraw Scar Limestone
II Gayle Limestone
I Hawes Limestone
Names have not been applied to the thin impersistent limestones, which are
designated by an index number, indicating the major cyclothem to which they belong,
and by an index letter, showing their position in the cyclothem.

BRITISH AVONIAN CONODONT FAUNAS 27

Moore (1958 : 95) described the major limestone at the base of the cyclothems and
grouped the other beds of the cyclothems together under the term " Non-Calcareous
Measures" (although they sometimes contain thin limestones and calcareous shales).

The lower boundary of the Yoredale Formation in the type area was placed by
Moore at the base of a thin sandstone-shale sequence, the Thorny Force Sandstone,
which lies below the Hawes Limestone. As pointed out by Walker (1964 : 210)
this lowest cyclothem is poorly exposed and is confined to a small geographical area.
The Girvanella Bed, which is accepted as the Di-D 2 boundary and hence roughly as
the B2-Pi a boundary of the goniatite sequence, in the middle of the Hawes Lime-
stone, is in this study taken as the base of the Yoredale Formation.

The Hawes Limestone, which is forty feet thick, may be divided into two distinct
members, a lower group of pale grey massive limestones, with pseudobreccias and a
fauna of compound corals, and an upper group of blue-grey thinly bedded limestones
with few fossils. The boundary between the two is the Girvanella Bed, which
lithologically is part of the upper group.

The Gayle Limestone, fifty-seven feet thick, may be divided into three parts. At
the base is a group of wavy-bedded limestones with irregular shale partings. A
massive bed, comparable in thickness to the whole of the underlying thin beds, forms
the middle group. The upper part of the Gayle Limestone consists of massively-
bedded, blue-grey, poorly-fossiliferous limestones.

The Hardraw Scar Limestone, twenty-five feet thick, consists in the lower half of
massive crinoidal limestones, often six feet thick at the base, which pass upwards
into thinly-bedded, calcite mudstones. The upper part of the Hardraw Scar Lime-
stone is more uniform than the lower, consisting of massive crinoidal limestones with
partings of rubbly limestone, which pass up into finer-grained limestones and fine-
grained calcite mudstones, which are partially dolomitised.

Limestone III A is a fine-grained limestone containing corals (Lithostrotion) .
Limestone III B is arenaceous and almost unfossiliferous, whereas Limestone III C
is less sandy and contains small crinoids.

The Simonstone Limestone, which is fifteen feet thick, consists in the lower part of
a clastic limestone phase, with the development of coarse crinoidal limestones and
sandy limestones with a sporadic fauna at the base, which passes upwards into a fine
grained limestone and calcareous shale fades which often contains compound corals.
The upper part of the Simonstone Limestone consists of fine grained limestone at the
base, overlain in turn by coarsely crinoidal limestones and fine grained algal lime-
stones.

Limestone IV A, three feet thick, is a fine grained limestone, which is sandy at the
base. Limestone IV B is a fine grained argillaceous limestone, z\ feet thick, with a
9" bed of shale in the middle.

The Middle Limestone, 65 feet thick, is divisible into three thick limestone units,
each separated by shales and thin limestone bands.

The Five Yard Limestone, two feet thick, consists of fine grained limestones,
sparingly crinoidal, but with a rich fauna of corals and brachiopods. This formation

BRITISH AVONIAN CONODONT FAUNAS

is usually developed in two beds with a parting of calcareous shale which has an
abundant fauna.

The Three Yard Limestone, which is eight feet thick, is a crinoidal fine grained
limestone.

Walker (1964 : 210) suggested that since a continuously exposed section through
the whole Yoredale Formation did not exist in the type area, two sections, one
representing the upper part and the other the lower part of the Formation, should be
taken as type sections. Although Walker's section exposes the beds of his redefined
Yoredale Series, it does not include the lower beds of the Yoredale Formation (as
defined by Moore 1958). Walker described the upper part of the Formation, from
the base of the Hardraw Scar Limestone to the top of the Underset Limestone, as
exposed in Long Sike and North Scar Gill at the head of Snaizeholme Valley
(SD/815840) which is west of the town of Hawes. The lower part of the Formation,
from the base of the Hawes Limestone to the base of the Hardraw Scar Limestone,
outcrops 3^ miles towards the north east in Gayle Beck (SD/864883), which is near the
town of Hawes. The Hardraw Scar Limestone, according to Walker, forms a topo-
graphic feature, which can be traced from the base of the first section to the top of the
second, and this establishes the relative stratigraphic position of the two sections.

In order to apply the conodont zonation established in south west England to
northern England, fifteen samples, one or more being taken from each of the main
limestones at the above localities, were processed.

Fig. 8. Outline map of the Wensleydale area, North Yorkshire, from which the Yoredale
succession was collected.

BRITISH AVONIAN CONODONT FAUNAS

(v) Scotland

Rocks of Carboniferous age outcrop over much of the Midland Valley of Scotland.
Strata of " Lower " Carboniferous age lie below the Passage Group and Productive
Coal Measures of the typical coalfield areas, but in places both the Passage Group and
the Oil Shale Groups are replaced by contemporaneous lavas, chiefly of olivine
basaltic composition.

These strata were traditionally subdivided into two broad lithological series,
the Calciferous Sandstone Series and an overlying Carboniferous Limestone
Series. The lower of these divisions is now termed the Calciferous Sandstone
Measures, and the upper division is no longer used on maps of the Geological Survey
(MacGregor i960). The lowest division of the Calciferous Sandstone Measures, the
Cementstone Group, consists of alternating fine-grained dolomite and shales, whilst
the overlying Lower and Upper Shale Groups consist of alternating series of sand-
stones, shales, coals, fireclays and limestones. Both marine and fresh-water lime-
stones occur and oil shales are widespread . The greatest thickness of the Groups is
in the East Fife Coalfield where some 4,000 ft. of strata occur.

The overlying strata (the " Carboniferous Limestone Series " of earlier authors)
are subdivided into three lithological groups, the Lower Limestone Group, the Lime-
stone Coal Group, and the Upper Limestone Group. The two higher groups each
have a maximum thickness of some 1,500 ft. in the West Fife Coalfield, while the
maximum thickness of the Lower Limestone Group is only some 700 ft. Like the
Calciferous Sandstone Measures, the whole Carboniferous Limestone " Series " thins
rapidly southwestwards into the North Ayrshire Coalfield, where it is reduced in
places to less than 100 ft. The Lower Limestone Group consists of thin marine

Fig. 9. Outline map of Southern Scotland, showing localities mentioned in the text.

30 BRITISH AVONIAN CONODONT FAUNAS

limestones, including the Hosie Limestones, and inter-bedded shales, with sub-
ordinate ironstone nodules and coals. Alternating sandstones, shales, fireclays, and
workable coals and ironstones mark the Limestone Coal Group, while the Upper
Limestone Group consists predominantly of sandstone, with subordinate shales,
limestones and coals.

I. Dunbar. Samples were collected from limestone bands within the Lower
Limestone Group near Catcraig (NT 715772). The beds collected were the Long
Craig Upper (NT 749752), Skateraw Lower (NT 748752), Skateraw Middle (NT
743754), Skateraw Upper (NT 738758), Chapel Point (NT 722774), Barness East
(NT 724773) and the Dryburn Foot (NT 732763) Limestones.

II. Midlothian. The Lower Limestone Group was collected from various points
in the Midlothian Coalfield. The " Gilmerton " Limestone was collected i| miles
S.S.E. of Carlops (NT 172544) where it consists of grey crystalline limestone and
shales, with a limestone breccia at the top. The North Greens Limestone was
collected in Bilston Burn (NT 270649) and in the banks of the River North Esk,
250 yds. S.W. of Newhall House. It consists of about 35 ft. of impure, thinly-
bedded, argillaceous limestone.

The Vexhim Limestones were collected in Glencorse Burn, 350 yds. upstream from
Milston Bridge (NT 250628).

The overlying Bilston Burn Limestone was collected in Bilston Burn, where it
consists of about 40 ft. of thinly-bedded limestone, with an overlying bed of cal-
careous shale and a 5 ft. bed of dolomitic limestone.

III. Fife. A thick succession of the Calciferous Sandstone Measures and the
Lower Limestone Group is exposed (Figs 85, 86) near Pittenweem (NO 548027) on
the shore of the Firth of Forth, between Anstruther and Coal Farm. Samples
were collected from the limestone and shale beds, the limestones yielding abundant
conodonts, whereas the Calciferous Sandstone Measures, apart from three beds
( x 5» 43' 3^8), were barren.

IV. Ayrshire. Sections through the Lower Limestone Group and the Upper
Limestone Group were collected.

The Broadstone Limestone was collected at Auchenmade (NS 342486) where it is
overlain by the Dockra Limestone, which was also collected here. The Hosie Lime-
stones were collected in a railway cutting at Glengarnock (NS 333525).

In the Upper Limestone Group the Index Limestone was collected near Glonbeith
Castle (NS 332458) and near Drumbuie House (NS 361506) where it was about six
feet thick.

The Lower and Upper Linn Limestones were collected at the Linn Spout near
Dairy (NS 287487, NS 284485).

V. Roxburghshire. The Main Algal ' Series ' of Garwood (1931) was collected in
Harden Burn (NY 517907) and the limestone bands, apart from the algal bed,
yielded abundant conodonts.

VI. Argyll. The Carboniferous Limestone 'Series' at Machrihanish (McCallien
1928 ; McCallien & Anderson 1930) was examined and the limestones were collected
where they were exposed on the beach (NR 632208).

BRITISH AVONIAN CONODONT FAUNAS 31

The general geology of the Scottish collecting areas is described in the following
publications : Carruthers et al. (1927), Clough et al. (1925), Craig (1965), Currie
(1954), Dinham & Holdane (1932), Goodlet (1957), George (1958), Mitchell &
Mykura (1962), Richey et al. (1930), Robertson et al. (1949) and Tulloch & Walton
(1958).

IV. METHODS OF STUDY

Samples were collected from the successions at intervals of 10 ft. and in many
parts of the sections these were supplemented by collections made at 5 ft. or 2 ft.
intervals. Most of the original samples from the reconnaissance survey weighed
about 25 lbs. but the samples from the smaller intervals weighed only 2-4 lbs.

These samples were weighed and then digested in 8% commercial acetic acid,
contained in plastic buckets. Shales were disintegrated with concentrated hydro-
gen peroxide, and formic acid was used for some of the limestones. After the rock
had dissolved, the sludge was sieved under water on 25, 50, 100 and 200 mesh
screens, the fractions being dried and then separated in bromoform.

The heavy residues were searched with a binocular microscope and the conodonts
picked and mounted (see Collinson 1963 for further details).

Photography was carried out by Mr. S. Osborn, using a Leitz Aristophot apparatus
and Adox KB 14 film, developed in Acutol or I.D. 48 developer. The specimens
were coated with ammonium chloride. Prints were cut out and mounted but no
retouching was undertaken.

V. CONODONT FAUNAS

(a) General Review

The present study is based upon 600 rock samples, and has involved the solution of
some 3 tons of rock, which yielded over 25,000 identifiable conodonts. We regard
this total collection as satisfactory, although the average abundance of conodonts
per kilogram of rock is considerably lower than the yields from some other areas.

The distribution of conodonts within the various sections studied was far from
uniform, and abundance ratios for each sample are included with each of the litho-
logical sections (Figs 59-92). The succession in the Avon Gorge illustrates the
problems involved in the less fossiliferous parts of the section. The average number
of conodonts per kilogram was 8 for the K Zone, with a range from 0-47 per kilogram.
In general the shales provided poor yields or were barren, while intervening lime-
stones were relatively fossiliferous. Shale samples 7 and 8, for example, were barren,
but they are separated by two thin limestones, yielding 20 and 16 conodonts per
kilogram.

The Z Zone consists predominantly of massive, blue-grey calcarenite, and has an
average yield of 19 conodonts per kilogram. There is again a fair range of variation
(0-66 per kg.), the lowest yields being in limestones with a high haematite content.
The upper beds of the Zone had high yields (45-66 per kg.).

In contrast, the Lower Ci, the Laminosa Dolomite, yielded an average of only 3
conodonts per kilogram, probably reflecting either the destructive results of second-

32 BRITISH AVONIAN CONODONT FAUNAS

ary dolomitisation, or possibly an unfavourable depositional environment, while the
upper Ci Caninia Oolite had an average yield of only i conodont per kilogram (range
0-3 per kg.). Other conodont students have commonly found lithologically similar
oolites to have low yields, and this may be the result of relatively rapid deposition.
Of the 23 samples of the Caninia Dolomite which were processed, only one, a shelly
calcarenite, yielded conodonts.

S Zone samples had a yield of less than 1 per kilogram, and almost three quarters
of the 72 samples processed were barren. Only 5 samples yielded an average of more
than one conodont per kilogram. The Zone is marked by relatively little change in
the conodont faunas, and, like the low yielding (1 per kg.) D Zone beds, probably
represents rapidly deposited sediments.

Broadly comparable variations in abundance are seen in strata of similar litho-
logies from other sections. In the D Zone of South Wales, for example, the mean
yield was 29 conodonts per kilogram of limestone dissolved, with a range from 0-198.
In the Z Zone of the North Crop, the mean yield was 9 conodonts per kilogram, with
a range from 0-60. In general the lowest yields were those of the saccharoidal
dolomites, and the highest were those of the basal beds of oolites.

(b) Stratigraphical distribution of conodont faunas

The precise ranges of all conodont species recovered for each of the various areas
are shown on Figs. 49-58. The present section provides only a general view of
the distribution of some of the more useful genera and species.

Patrognathus gen. nov. is restricted to the K Zone. The genus Clydagnathus gen.
nov. is found in the K Zone and in the lower part of the Z Zone of the North Crop and
in Shropshire. It is rare in large faunas of the same age from the Avon Gorge,
although it occurs abundantly in some other countries, e.g. Australia. The lowest
occurrence of the genus is represented by the species C. gilwernensis gen. et sp. nov.
and C. cavusformis gen. et sp. nov., which are rapidly replaced by Clydagnathus sp. A
gen. et sp. nov. The Lower Z Zone species are C. unicornis gen. et sp. nov. and C.
darensis gen. et sp. nov. The genus Siphonodella, which has proved to be abundant
and of great stratigraphical value in other areas, is rare in the Avonian. It is con-
fined to the upper part of the K Zone in both the Avon Gorge and the North Crop.
The limited stratigraphic range of the genus in the Avonian is also reflected in an
absence of the sequence of species, which has been described from the Mississippi
Valley.

The genus Pseudopolygnathus is one of the most distinctive components of the
faunas of the K and Z Zones, extending from the base of the K Zone into the Ci
Laminosa Dolomite. It is represented by a considerable number of species, most of
which have restricted stratigraphical ranges. Pseudopolygnathus vogesi sp. nov. and
Pseudopolygnathus expansus sp. nov. are confined to the lowest part of the K Zone,
where they are distinctive species. The Z Zone is characterized by the incoming of
abundant pseudopolygnathids, referable to the species P. primus Branson & Mehl
and P. cf. dentilineatus E. R. Branson. These are replaced vertically by P. postino-
dosus sp. nov. and P. nodomarginatus E. R. Branson. In contrast to the abundance

BRITISH AVONIAN CONODONT FAUNAS

Feet
180

160-

140

120

100-

40-

20-

100

60-

20-

Distribution and relative abundance of species of
S patho g nathodus and related genera.

Pseudopolygnathus sp.

S.tndentatus S.crassidentatus

S.costatus - , ,
sulciferus S.costatusss.

S.plumulus ss

Clydagnathus
cavusensis

S.plumulus
nodosus

Pseudopolygnathus
vogesi

Splumulu
shirleyoel

S.elongatus

S.anteposicorni!

Scf. robust us

Scyrius

I „ (

Percenta g e of
total conodont
fauna

0-1 °/o

1-5°/o
5-15"».J
15-30°/«

>30°/o|

Fig. io. Distribution and relative abundance of species of Spathognathodus and related
genera in the Z and K Zones of the Avonian of the North Crop.

34 BRITISH AVONIAN CONODONT FAUNAS

of Pseudopolygnathus in the Lower Z Zone of the Avon Gorge, the genus is absent in
strata of similar age from the North Crop. In these latter faunas it is presumably
represented by functional homoeomorphs in the natural conodont assemblages.
These could well be spathognathodids, from which Pseudopolygnathus seems to have
arisen. The Lower Z Zone assemblage is replaced by abundant P. multistriatus Mehl
& Thomas near the base of the Z2 Subzone, which is in turn replaced by abundant
P. longiposticus (Branson & Mehl) towards the top of the Z2 Subzone. The genus is
rare in the Lower Ci Subzone.

The genus Gnathodus is one of the longest ranging in the Avonian, but its restricted
and distinctive species have been particularly useful in some of our correlations. Its
oldest occurrence is near the base of the Z2 Subzone, where G. delicatus Branson &
Mehl is found. On the North Crop, G. simplicatus sp. nov. also occurs in Lower Z
Zone faunas. G. delicatus is associated near the top of the Z2 Subzone with G. semi-
glaber (Bischoff), a distinctive Upper Z Zone species, which is in turn replaced by G.
antetexanus Rexroad & Scott at the top of the Z Zone. G. punctatus (Cooper), G.
avonensis sp. nov. and G. simplicatus sp. nov. also occur in the Upper Z Zone. A
single specimen of G. cuneiformis Mehl & Thomas was collected in the middle of the
Si Subzone. Gnathodus is rare or absent in the higher C and S faunas, but is
represented by several distinctive species in the D Zone. G. bilineatus (Roundy)
appears at the base of the D2 Subzone, together with G. girtyi girtyi Hass. In the
highest part of the D2 Subzone G. girtyi simplex Dunn, G. commutatus (Branson &
Mehl), G. mononodosus sp. nov. and G. homopunctatus Ziegler appear. G. girtyi
collinsoni sub. sp. nov. appears in the middle of the D 3 Subzone, and G. girtyi
turritus Collinson & Druce near the top (Fig. 11).

The genus Spathognathodus has an extended range, being present throughout the
Avonian. The dominant species of the Lower K Zone is S. plumulus sp. nov., which
is represented by several subspecies. The Upper K Zone is marked by a variety of
spathognathodids, including S. elongatus (Branson & Mehl), Spathognathodus cf.
robustus (Branson & Mehl), 5. anteposicornis Scott, and 5. tridentatus (E. R. Branson).
The three former species, though never abundant, extend into the Lower Z Zone,
while the latter, together with S. crassidentatus, which first appears in the basal K
Zone, is abundant in the Lower and Middle Z Zone. S. costatus costatus (E. R.
Branson) and S. costatus sulciferus (Branson & Mehl) appear in the Lower Z Zone in
the North Crop and are abundant in the middle part of the Zone. S. cyrius (Cooper),
a rare species throughout the K and Lower Z Zones, overlaps the lower occurrence of
these species, and S. cf. cristulus Youngquist & Miller is also present, extending
upwards into the C Zone. S. pulcher Branson & Mehl occurs high in the Z Zone and
5. coronus sp. nov. in the C Zone. S. scitulus (Hinde) is present in the Caninia
Oolite and extends into the D Zone. S. cristulus Youngquist & Miller is character-
istic of the D2 Subzone and S. campbelli Rexroad of the D3.

Polygnathus first appears near the base of the K Zone and extends to the top of Ci.
Polygnathus communis Branson & Mehl extends from near the base of the K Zone to
the middle of the Laminosa Dolomite. Polygnathus inornatus inornatus Branson &
Mehl, P. lobatus lobatus Branson & Mehl, P. inornatus rostratus subsp. nov., P.

RANGES OF IMPORTANT
SPECIES OF CNATHODUS

C 2 S,

1 r

No gnathodids

BRITISH AVONIAN CONODONT FAUNAS 35

inornatus vexatus subsp. nov. and P. lobatus inflexus subsp. nov. appear in the Middle
K Zone. The P. inornatus group becomes extinct in the upper part of the K Zone.
The P. lacinatus Huddle group appears in the uppermost Z Zone, together with P.
lacinatus asymmetricus subsp. nov. The C Zone is characterized by P. lacinatus s.s.
and P. bischoffi sp. nov.

The genus Mestognathus first appears in the upper part of the Ci Subzone, where it
is represented by M. beckmanni Bischoff, which extends into the D Zone. M . bipluti
Higgins first appears in the Di Subzone and extends into the higher part of D2, where
M. neddensis sp. nov. is also present. Neither extends into the D 3 Subzone.

Cavusgnathus is most characteristic of the C2, S and D Zones. C. unicornis
Youngquist & Miller is present in the C2 Caninia Dolomite and extends into the D
Zone. C. charactus Rexroad first occurs in the C2S1 Zone, and C. convexus Rexroad
is characteristic of the Middle S Zone.

The genus Taphrognathus is restricted to the Upper S2 Subzone, where it is
represented by a single species, T. varians Branson & Mehl.

The striking genera Bactrognathus, Doliognathus, Scaliognathus and Staurognathus,
which are distinctive components of faunas of comparable age in other areas, are
unrepresented in our Avonian faunas, in which the genus Elictognathus is represented
by only a single fractured specimen. It seems probable that these genera were
geographically or ecologically restricted.

Most of the genera of " bars and blades " have a long stratigraphic distribution,
but a number of species have proved valuable in local correlation. Ligonodina beata
nom. nov., Hindeodella corpulenta Branson & Mehl, and H. subtilis Ulrich & Bassler
are common Upper K and Z Zone forms. Apatognathus makes its first appearance in
the Z2 Subzone. A. geminus (Hinde) is present in the Ci Subzone and extends into
the D Zone. A. scalenus Varker appears in the Upper Ci Subzone. A. bladus sp.
nov. is confined to the D2 Subzone. Prioniodina laevipostica (Rexroad & Collinson)
is limited to the Upper D2 Subzone. N eopHoniodus scitulus (Branson & Mehl), N.
peracutus (Hinde), Hindeodella undata Branson & Mehl, and H. antecomplex Collinson
& Druce first appear in the Lower D3 Subzone. Magnilaterella clarkei sp. nov. is
confined to the D Zone, as is Kladognathus.

The precise ranges of these and other species are given on Figs. 49-58. The low
yield of conodonts from many samples makes reliance upon any single " index fossil "
an unreliable method of correlation, but the general characteristics of the individual
conodont assemblages are distinctive for each of our main stratigraphic divisions,
and these provide the basis of a relatively precise scheme of correlation.

A series of 14 conodont assemblage zones has been established. We have used the
Avon Gorge and the North Crop successions as our type sections, using the latter to
provide the three highest Avonian Zones, which are largely represented by non-
carbonate sediments in the Avon Gorge area. We have therefore included in this
section a detailed discussion of the correlation between these two areas, in order to
provide a basis for the zonal scheme, which we have used (p. 46) to establish correla-

BRITISH AVONIAN CONODONT FAUNAS

tions between these type sections and Avonian sequences in Central England and
Scotland. We believe that these conodont zones provide a useful method of
correlation throughout the British Avonian, and that they offer a considerably
higher degree of precision than existing coral-brachiopod zones.

They show no detailed correspondence to the conodont zones established in either
the Mississippi Valley or in West Germany, although the general faunal sequence in
the three areas has enough broad resemblances to allow us to correlate between them
with some confidence.

The sequence and relationship of the 14 zones are shown in Fig. 12. They
are defined and described below, and the detailed correlation between the Avon
Gorge and the North Crop is discussed. The intercontinental correlations given for
each zone below are generalized and approximate. There is a full discussion of
correlation on p. 52.

Patrognathus variabilis — Spathognathodus plumulus Assemblage Zone

Characteristic species : Patrognathus variabilis gen. et sp. nov., Spatho-
gnathodus plumulus plumulus sp. nov., Pseudopolygnathus vogesi sp. nov., Spatho-
gnathodus plumulus shirleyae sp. et subsp. nov. and, in North Crop, Clydagnathus
gilwernensis gen. et sp. nov.

Limits : The base of the assemblage zone is not identified, but probably corres-
ponds to the first appearance of P. variabilis gen. et sp. nov. The upper limit
coincides with the oldest stratigraphic occurrence of Polygnathus inornatus inornatus
Branson & Mehl, Polygnathus lobatus lobatus Branson & Mehl, and also of the genus
Siphonodella.

Remarks : This zone occupies the lower and middle of the K Zone (Samples K 1-
K 11 in the Avon Gorge and Samples KL i-KL 13 on the North Crop). It is
correlated with part of the Cu I of West Germany, the lower and middle parts of the
Hannibal Formation of North America and with the Tn2b and Lower Tn2 C of Belgium.

The lowest Lower Limestone Shale, which immediately overlies the Old Red
Sandstone in the Avon Gorge, does not contain conodonts. The basal limestone
stratum (Sample K 3) is characterized by the presence of S. plumulus plumulus
subsp. nov. and P. variabilis gen. et sp. nov. Sample K 4 is the oldest from the
Avon Gorge to contain pseudopolygnathids, whereas these pseudopolygnathids
occur in the North Crop in the basal beds of the Lower Limestone Shale which
directly overlies the Old Red Sandstone.

Fig. 13. Chart to show the characteristic species of the conodont zones proposed in the
present paper. Where a species is shown breaking the boundary between two successive
zones, it is present in both.

Patrognathus variabilis — Spathognathodus plumulus Assemblage Zone. ia. Patrognathus
variabilis gen. et sp. nov. — oral view. ib. Patrognathus variabilis gen. et sp. nov. —
lateral view. 2a. Spathognathodus plumulus plumulus sp. nov. — lateral view. 2b.
Spathognathodus plumulus plumulus sp. nov. — oral view. 3a. Pseudopolygnathus
vogesi sp. nov. — oral view. 3b. Pseudopolygnathus vogesi sp. nov. — aboral view.
4a. Spathognathodus plumulus shirleyae subsp. nov. — lateral view. 4b. Spathognathodus

"tllll"

"";r::.:r

»» = »-

T.°.r

....... ........ .....

:r».

-H°r

........

•=.- -»•»-

,„

°,

EF"'

c.S,

.....................

c.m-

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WARS.*

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...,....,,.....,.,.....,..,...

...........

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cuiui-if

...

;r."«™. L .°"™

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......„,„..,.;. „.„,„„.,.,

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..... .......

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:> i J 2i.fi.Lt ion Hi tlit Avoni.m nn the bails i.f .:..n.").>nts. shewing tlit relatiniiship ol the zones proposed in this paper to the cor;ii/brachiopod
divisions ..I the Avon Gorjje, and tht North Crop, and also the relationship of the Yorcdalc strata in the upptr p.irt .if the succession. A
comparison is made with the conodont zones established in the Mississippi Valley and wiih the Hematite /.one* of Europe.

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BRITISH AVONIAN CONODONT FAUNAS 37

plumulus shirleyae subsp. nov. — oral view. 5a. Clydagnathus gilwernensis gen. et sp.
nov. — oral view. 5b. Clydagnathus gilwernensis gen. et sp. nov. — lateral view.

Siphonodella — Polygnathus inornatus Assemblage Zone. 6a. Polygnathus inornatus
inornatus — lateral view. 6b. Polygnathus inornatus inornatus — oral view. 7a. Poly-
gnathus lobatus lobatus — oral view. 8. Polygnathus lobatus inflexus — oral view. 9a. Poly-
gnathus inornatus rostratus — oral view. 9b. Polygnathus inornatus rostratus — aboral view.
10a. Siphonodella isosticha — aboral view. 10b. Siphonodella isosticha — oral view.
Spathognathodus cf. robustus — S. tridentatus Assemblage Zone. n. Spathognathodus
cf. robustus — lateral view. 12. Spathognathodus elongatus — lateral view. 13a. Spatho-
gnathodus tridentatus — lateral view. 13b. Spathognathodus tridentatus — oral view.
13c. Spathognathodus tridentatus — aboral view. 14. Spathognathodus crassidentatus —
lateral view. 15. Spathognathodus anleposicornis — lateral view.

Spathognathodus costatus costalus — Gnathodus delicatus Assemblage Zone. 16a. Spatho-
gnathodus costatus costatus — lateral view. 16b. Spathognathodus costatus costatus — aboral
view. 17a. Spathognathodus costatus sulciferus — lateral view. 17b. Spathognathodus
costatus sulciferus — oral view. 18a. Spathognathodus cf. cristulus — lateral view.
18b. Spathognathodus cf. cristulus — oral view. 19. Spathognathodus cf. cyrius — lateral
view. 20a. Gnathodus delicatus — lateral view. 20b. Gnathodus delicatus — oral view.
21. Ligonodina beata nom. nov. — inner lateral view. 22. Hindeodella corpulenta — lateral
view. 23. Hindeodella subtilis — lateral view. 24a. Pseudopolygnathus primus — oral
view. 24b. Pseudopolygnathus primus — aboral view. 25. Pseudopolygnathus cf.
dentilineatus — oral view. 26a. Pseudopolygnathus multistriatus — aboral view. 26b.
Pseudopolygnathus multistriatus — oral view. 27. Gnathodus simplicatus sp. nov. — oral
view. 28a. Clydagnathus unicornis gen. et sp. nov. — oral view. 28b. Clydagnathus
unicornis gen. et sp. nov. — lateral view. 29a. Pseudopolygnathus postinodosus sp. nov. —
oral view. 29b. Pseudopolygnathus postinodosus sp. nov. — lateral view.

Polygnathus lacinatus Assemblage Zone. 30. Polygnathus lacinatus lacinatus — oral
view. 31a. Polygnathus lacinatus asymmetricus subsp. nov. — lateral view. 31b. Poly-
gnathus lacinatus asymmetricus subsp. nov. — oral view. 32. Polygnathus nodomarginatus —
oral view. 33a. Cavusgnathus sp. nov. A. — oral view. 33b. Cavusgnathus sp. nov.
A. — lateral view. 34. Pseudopolygnathus multistriatus — oral view.

Polygnathus lacinatus — Pseudopolygnathus cf. P. longiposticus Assemblage Zone.
35. Gnathodus semiglaber — oral view. 36a. Gnathodus delicatus — lateral view. 36b.
Gnathodus delicatus — oral view. 37. P. cf. longiposticus — lateral view. 38. Polygnathus
lacinatus lacinatus — oral view. 39a. Spathognathodus pulcher — oral view. 39b. Spatho-
gnathodus pulcher — lateral view. 40. Gnathodus simplicatus sp. nov. — oral view. 41a.
Gnathodus avonensis sp. nov. — oral view. 41b. Gnathodus avonensis sp. nov. — lateral
view.

Gnathodus antetexanus — Polygnathus lacinatus Assemblage Zone. 42. Apatognathus
geminus — inner lateral view. 43. Apatognathus scalenus — inner lateral view. 44.
Apatognathus petilus — outer lateral view. 45a. Spathognathodus cf. cristulus — lateral
view. 45b. Spathognathodus cf. cristulus — oral view. 46. Gnathodus antetexanus — oral
view.

Mestognathus beckmanni — Polygnathus bischoffi Assemblage Zone. 47a. Mestognathus
beckmanni — lateral view. 47b. Mestognathus beckmanni — oral view. 48a. Polygnathus
bischoffi sp. nov. — oral view. 48b. Polygnathus bischoffi sp. nov. — aboral view.

Cavusgnathus unicornis — Apatognathus Assemblage Zone. 49. Cavusgnathus unicornis
— inner lateral view. 50a. Spathognathodus cristulus — lateral view. 50b. Spathognatho-
dus cristulus — oral view. 51a. Mestognathus beckmanni — inner lateral view. 51b.
Mestognathus beckmanni — oral view. 52a. Gnathodus cuneiformis — oral view. 52b.
Gnathodus cuneiformis — lateral view. 53a. Cavusgnathus charactus — oral view. 53b.

[Caption to Fig. 13 continued on p. 38

38 BRITISH AVONIAN CONODONT FAUNAS

In addition, on the North Crop two subzones can be delineated, the lower being
characterized by the presence of Spathognathodus plumulus nodosus sp. et subsp. nov.,
Clydagnathus gilwernensis gen. et sp. nov. and Psendopolygnathus vogesi sp. nov.
The upper is recognized by the absence of the above-mentioned species and by the
presence of Clydagnathus sp. nov. A.

Siphonodella — Polygnathus inornatus Assemblage Zone

Characteristic species : Polygnathus inornatus inornatus Branson & Mehl,
Polygnathus lobatus lobatus Branson & Mehl, Polygnathus lobatus inflexus subsp. nov.,
Polygnathus inornatus rostratus subsp. nov. and Siphonodella isosticha (Cooper).

Limits : The base of this zone is marked by the first occurrence of Siphonodella
isosticha (Cooper), P. inornatus inornatus Branson & Mehl, P. lobatus lobatus Branson
& Mehl, and P. inornatus rostratus subsp. nov. The top of the zone is marked by the

Continuation of Fig. 13 caption]

Cavusgnathus charactus — inner lateral view. 54a. Cavusgnathus cristatus — inner lateral
view. 54b. Cavusgnathus cristatus — oral view.

Taphrognathus varians — Cavusgnathus — Apatognathus Assemblage Zone. 55a.
Taphrognathus varians — oral view. 55b. Taphrognathus varians — lateral view. 56a.
Spathognathodus cristulus — oral view. 56b. Spathognathodus cristulus — lateral view.

Apatognathus ? geminus — Cavusgnathus Assemblage Zone. 57a. Cavusgnathus
cristatus — inner lateral view. 57b. Cavusgnathus cristatus — oral view. 58. Apato-
gnathus ? geminus — inner lateral view.

Mestognathus beckmanni — Gnathodus bilineatus Assemblage Zone. 59a. Mestognathus
beckmanni — inner lateral view. 59b. Mestognathus beckmanni — oral view. 60. Cavus-
gnathus unicornis — inner lateral view. 61. Spathognathus scitulus — lateral view.
62a. Apatognathus bladus sp. nov. — inner lateral view. 62b. Apatognathus bladus sp.
nov. — outer lateral view. 63. Hibbardella abnormis — inner lateral view. 64. Neo-
prioniodus singularis — lateral view. 65a. Gnathodus girtyi girtyi — oral view. 65b.
Gnathodus girtyi girtyi — lateral view. 66a. Gnathodus bilineatus — oral view. 66b.
Gnathodus bilineatus — lateral view.

Gnathodus mononodosus Assemblage Zone. 67a. Gnathodus girtyi simplex— lateral
view. 67b. Gnathodus girtyi simplex — oral view. 68a. Gnathodus mononodosus sp.
nov. — lateral view. 68b. Gnathodus mononodosus sp. nov. — oral view. 68c. Gnathodus
mononodosus sp. nov. — aboral view. 69a. Gnathodus commutatus — lateral view. 69b.
Gnathodus commutatus — oral view. 70a. Gnathodus homopunctatus — lateral view. 70b.
Gnathodus homopunctatus — oral view. 71a. Spathognathodus cf. cristulus — lateral view.
71b. Spathognathodus cf. cristulus — oral view.

Gnathodus girtyi collinsoni Assemblage Zone. 72a. Gnathodus girtyi collinsoni subsp.
nov. — oral view. 72b. Gnathodus girtyi collinsoni subsp. nov. — lateral view. 73a.
Gnathodus girtyi simplex — oral view. 73b. Gnathodus girtyi simplex — lateral view.
74a. Gnathodus girtyi girtyi — oral view. 74b. Gnathodus girtyi girtyi — lateral view.
75a. Gnathodus nodosus — lateral view. 75b. Gnathodus nodosus — lateral view. 75c.
Gnathodus nodosus — -aboral view. 76a. Gnathodus mononodosus sp. nov. — lateral view.
76b. Gnathodus mononodosus sp. nov. — oral view. 76c. Gnathodus mononodosus sp. nov. —
aboral view. 77a. Gnathodus bilineatus — oral view. 77b. Gnathodus bilineatus — lateral
view. 78. Prioniodina stipans — lateral view. 79. Prioniodina subaequalis — lateral view.
80. Neoprioniodus scitulus — lateral view. 81. Neoprioniodus tulensis — lateral view.
82. Ligonodina levis — inner lateral view.

BRITISH AVONIAN CONODONT FAUNAS 39

first appearance of Spathognathodus cf. robustus (Branson & Mehl), S. tridentatus
(E. R. Branson) and S. anteposicornis Scott.

Remarks : This zone occupies nearly all the Upper K Zone in the North Crop
and the lower part of the Upper K Zone in the Avon Gorge (Samples K 12-K2I in the
Avon Gorge and Samples KL 16-KL 18 on the North Crop). It is correlated with
the Upper Cu I and basal Cu II a of West Germany, the lower part of the Upper
Hannibal Formation of North America and with part of the Tn2 C of Belgium.

On the North Crop a covered shale interval is present between Samples KL 13
and KL 16. In the Avon Gorge Samples K 12-K 17 contain P. variabilis gen. et sp.
nov. and S. piumulus s.s. sp. nov., associated with the P. inornatus group. On the
North Crop (Samples KL 16-KL 18) P. variabilis gen. et sp. nov. and S. piumulus s.s.
sp. nov. are absent from the zone. 5. isosticha (Cooper) has not been found in the
Avon Gorge, but there is a concealed interval above K 17 and below K2I. There
are thus two subzones within this assemblage zone. The lower corresponds to
Samples K 12-K 17 in the Avon Gorge and occupies the covered interval between
KL 13 and KL 16 on the North Crop ; the upper subzone (KL 16-KL 18 of the
North Crop) occupies the concealed interval above K 17 and below K2I in the
Avon Gorge.

Spathognathodus cf. robustus — Spathognathodus tridentatus

Assemblage Zone

Characteristic species : S. cf. robustus (Branson & Mehl), S. elongatus (Branson
& Mehl), 5. tridentatus (E. R. Branson), S. crassidentatus (Branson & Mehl) and S.
anteposicornis Scott.

Limits : The base of this zone is marked by the first occurrence of Spathognathodus
cf. robustus (Branson & Mehl), 5. tridentatus (E. R. Branson) and S. anteposicornis
Scott.

The top of the zone is marked by the first occurrence of Spathognathodus costatus
costatus (E. R. Branson). The final appearance of the Polygnathus inornatus group
is within the lower part of the zone.

Remarks : This zone occupies the upper part of the Upper K Zone in the Avon
Gorge (Sample K21) and the uppermost K and basal Z Zone on the North Crop
(Samples KL 19-ZLA 1). It is correlated with the upper part of the Hannibal
Formation of North America, with the Lower Cu II a of Germany and with the
Upper Tn 2c of Belgium (see also p. 56).

The lower part of this zone (with the P. inornatus group) probably occurs in the
concealed interval beneath Sample K2I in the Avon Gorge.

Spathognathodus costatus costatus — Gnathodus delicatus Assemblage Zone

Characteristic species : In both the Avon Gorge and the North Crop : S.
costatus costatus (E. R. Branson), S. costatus sulciferus (Branson & Mehl), 5. cf.
cristulus Youngquist & Miller, S. cyrius (Cooper), 5. crassidentatus (Branson & Mehl),
G delicatus Branson & Mehl, Ligonodina beata nom. nov., Hindeodella corpulenta

4 o BRITISH AVONIAN CONODONT FAUNAS

Branson & Mehl, Hindeodella subtilis Ulrich & Bassler. In the Avon Gorge :
Pseudopolygnathus primus Branson & Mehl, Pseudopolygnathus cf . dentilineatus E. R.
Branson, Pseudopolygnathus postinodosus sp. nov. On the North Crop : Clyda-
gnathus unicornis gen. et sp. nov., and Gnathodus simplicatus sp. nov.

Limits : The base of this assemblage zone is marked by the first occurrence of S.
costatus costatus (E. R. Branson) and 5. cf. cristulus Youngquist & Miller. The top of
the assemblage zone is recognized by the incoming of abundant Pseudopolygnathus
multistriatus Mehl & Thomas and by the replacement of G. delicatus Branson & Mehl
by G. semiglaber (Bischoff) and G. antetexanus Rexroad & Scott.

Remarks : This zone occupies the uppermost K, the Zi and the lower part of the
Z2 Subzones in the Avon Gorge and most of the Z Zone on the North Crop. (Avon
Gorge Samples K 18-Z 25 : North Crop Samples ZLA 2-ZLA 28). It is correlated
with the uppermost Hannibal, the Lower and Upper Chouteau Formation of North
America, with the Middle and Upper Cu II a of Germany, and with the uppermost
Tn2c and the Tn3 a of Belgium.

This assemblage zone shows some geographical differences. Spathognathodus
costatus costatus (E. R. Branson) first appears in the North Crop at the base of Sample
ZLA 2, some distance within the Z Zone, and is quickly followed by S. costatus
sulciferus (Branson & Mehl). In the Avon Gorge, on the other hand, these two
species are present in the uppermost beds of the K Zone. It is believed that Pseudo-
polygnathus primus Branson & Mehl evolved from S. costatus sulciferus Branson &
Mehl. In the Avon Gorge at the base of the Z Zone there is a burst of pseudopoly-
gnathids and the genus Pseudopolygnathus dominates the early Z Zone fauna. The
genus Pseudopolygnathus is not present in the Lower Z Zone in the North Crop, its
position in the natural conodont assemblages of the Z Zone on the North Crop being
represented by other form genera.

As a result, the following three subzones are recognized on the North Crop :
C. Clydagnathus unicornis (Samples ZL 11-ZLA 28).
B. Gnathodus simplicatus (Samples ZLA 15-ZL 10).

A. Spathognathodus costatus costatus-Spathognathodus costatus sulciferus
(Samples ZLA 2-ZLA 14).

The base of the Spathognathodus costatus costatus-Spathognathodus costatus
sulciferus Assemblage Subzone is marked by the first occurrence of S. costatus
costatus (E. R. Branson) and 5. cf. cristulus Youngquist & Miller. The subzone is
recognized by the presence of the above, together with S. costatus sulciferus (Branson
& Mehl), Gnathodus delicatus Branson & Mehl, and Apatognathus varians Branson &
Mehl. The Gnathodus simplicatus sp. nov. Assemblage Subzone is recognized by the
first occurrence of Gnathodus simplicatus sp. nov. and the presence of Gnathodus sp. B.
The top of this assemblage subzone is marked by the final occurrence of P. communis
Branson & Mehl, N. barbatus (Branson & Mehl), 5. costatus sulciferus (Branson &
Mehl) and A. varians (Branson & Mehl). The C. unicornis gen. et sp. nov.
Assemblage Subzone is marked by the paucity of the conodont fauna. What
fauna there is, is dominated by the presence of C. unicornis gen. et sp. nov., which up
to this point has been extremely rare. The top of this subzone is marked by the

BRITISH AVONIAN CONODONT FAUNAS 41

disappearance of 5. tridentatus (E. R. Branson), Clydagnathus darensis gen. et sp.
nov., C. unicornis gen. et sp. nov. and S. crassidentatus (Branson & Mehl).

In the Avon Gorge there are two subzones : a lower subzone characterized by the
presence of S. costatus costatus (E. R. Branson), 5. costatus sulciferus (Branson &
Mehl) and S. cf. cristulus Youngquist & Miller, with very few pseudopolygnathids
present, (Samples K 18-Z 9) and an upper zone of pseudopolygnathids (Samples
Z 10-Z 25). In the subzone of abundant pseudopolygnathids, Pseudopolygnathus
primus (Branson & Mehl) and Pseudopolygnathus cf. dentilineatus are abundant.
Pseudopolygnathus multistriatus Mehl & Thomas has its lowest stratigraphic occur-
rence in Sample Z 23.

Polygnathus lacinatus Assemblage Zone

Characteristic species : Polygnathus lacinatus s. s. Huddle, Polygnathus
lacinatus asymmetricus subsp. nov., Pseudopolygnathus nodomarginatus (E. R.
Branson), Spathognathodus pulcher Branson & Mehl and Pseudopolygnathus multi-
striatus Mehl & Thomas. Gnathodus antetexanus Rexroad & Scott, is present near
the base of the zone in the North Crop and at Farlow.

Limits : The lower limit is marked by the incoming of the P. lacinatus group and
of Gnathodus semiglaber (Bischoff). It is also a zone of abundant Pseudopolygnathus
multistriatus Mehl & Thomas. The upper limit is marked by the incoming of
Pseudopolygnathus cf. longiposticus (Branson & Mehl).

Remarks : This zone occupies the uppermost part of the Z sequence in the North
Crop and occurs near, but not at the top of, the Z Zone in the Avon Gorge, (North
Crop Samples ZLA 29-ZL 19 : Avon Gorge Samples Z 26-Z 32). It is correlated
with the unconformity at the base of the Sedalia Formation of North America, with
the lowest Cu II (3-y of Germany and with the base of Tn3 b of Belgium. The
presence of G. semiglaber and P. multistriatus in this zone indicates its broad equiv-
alence to the Sedalia Formation, but the fact that it also contains abundant G.
delicatus also implies a similarity to the underlying Upper Chouteau Formation.
These two formations are separated by an unconformity in the Mississippi Valley,
below which abundant G. delicatus occur, but above which this species is absent. It
seems probable that beds Z 26-28, in which the two groups of species overlap, are
broadly equivalent to the Chouteau-Sedalia unconformity time interval of the
Mississippi Valley (see also p. 59).

Polygnathus lacinatus — Pseudopolygnathus cf. longiposticus

Assemblage Zone

Characteristic species : G. semiglaber (Bischoff), G. delicatus Branson & Mehl,
P. cf. longiposticus (Branson & Mehl), Polygnathus lacinatus s.s. Huddle, Spatho-
gnathodus pulcher Branson & Mehl, Gnathodus simplicatus sp. nov. and Gnathodus
avonensis sp. nov.

Limits : The lower limit is marked by the lower limit of abundant P. cf. longi-
posticus (Branson & Mehl). It is also a zone of abundant Gnathodus. The upper

42 BRITISH AVONIAN CONODONT FAUNAS

limit is marked by the disappearance of P. cf. longiposticus (Branson & Mehl) and by
the replacement of G. semiglaber (Bischoff) by G. antetexanus Rexroad & Scott in the
Avon Gorge.

Remarks : This assemblage zone occupies the uppermost part of the Z Zone in
the Avon Gorge (samples Z 33-Z 38). It is absent, owing to an unconformity, in the
North Crop. It is correlated with the Fern Glen Formation of North America, the
Middle Cu II (3-y of Germany, and the Tn3 b in Belgium.

Gnathodus antetexanus — Polygnathus lacinatus Assemblage Zone

Characteristic species : Polygnathus lacinatus s.s. Huddle, Apatognathus
geminus (Hinde), Apatognathus scalenus (Varker), Apatognathus petilus Varker, S. cf.
cristulus Youngquist & Miller and G. antetexanus Rexroad and Scott.

Limits : The lower limit of the zone is marked by the youngest occurrence of P.
cf . longiposticus (Branson & Mehl) . The lower limit of the genus Apatognathus in the
Avon Gorge is near the lower limit of the zone. The upper limit of the zone is
marked by the oldest stratigraphic occurrence of Mestognathus beckmanni Bischoff.

Remarks : This zone occupies the lower part of the Ci Subzone in the Avon Gorge
(Samples C i-C 14). It is not present on the North Crop. It is correlated with the
lower, middle and lower upper parts of the Burlington Formation of North America,
with the upper part of Tn3 b and possibly the lowest Tn3 C of Belgium and with the
Upper Cu II (3-y of Germany.

In this assemblage zone conodonts are sparse. The genus Pseudopolygnathus is
represented by a considerably smaller number of specimens than in the underlying
zone. Specimens of the P. lacinatus group, S. cf. cristulus Youngquist & Miller and
A . scalenus (Varker) dominate the fauna. The youngest stratigraphic occurrence of
P. communis communis Branson & Mehl in the Avon Gorge is within this zone.

Mestognathus beckmanni — Polygnathus bischoffi Assemblage Zone

Characteristic species : Mestognathus beckmanni Bischoff, 5. cf. cristulus
Youngquist & Miller, Polygnathus bischoffi, sp. nov., A. scalenus Varker, A. petilus
Varker, and A. geminus (Hinde).

Limits : The lower limit of the zone is defined by the oldest stratigraphic
occurrence of Mestognathus beckmanni. The upper limit probably coincides with
the zone of maximum abundance of G. texanus (Roundy).

Remarks : This assemblage zone occupies the upper part of the Ci Subzone in the
Avon Gorge (Samples C 15-C 25). It is correlated with part of the Upper Burlington
Formation of North America, with the lowest Cu II 8 of Germany and with part of
the Tn3 C of Belgium.

The upper limit of this assemblage zone cannot be defined in the Avon Gorge,
because the lower beds of the Caninia Dolomite do not contain conodonts.

The conodont fauna obtained from the Upper Avonian C2, Si, S2, and D Zones of
the Avon Gorge is sparse in comparison with that obtained from the Lower Avonian.

BRITISH AVONIAN CONODONT FAUNAS 43

A gap is present in the conodont record of the lower part of the Caninia Dolomites
(Samples C 26-C 28). Dr. S. C. Matthews (personal communication) has a small
fauna of anchot ■alis-bilineatus interval aspect from an oolitic facies in the Mendips,
which represents the lateral equivalent of the Caninia Dolomite. This fauna
correlates with part of the Cu II S of Western Europe and with the Keokuk Formation
of North America.

Cavusgnathus unicornis — Apatognathus libratus Assemblage Zone

Characteristic species : Apatognathus libratus Varker, Cavusgnathus unicornis
Youngquist & Miller, 5. cristulus Youngquist & Miller, M. beckmanni Bischoff,
Gnathodus cuneiformis Mehl & Thomas, Cavusgnathus charactus Rexroad, and
Cavusgnathus cri status Branson & Mehl.

Limits : The lowest occurrence of the zone in the Avon Gorge coincides with the
oldest stratigraphic occurrence of Cavusgnathus unicornis Youngquist & Miller,
although the true base of the assemblage zone cannot be accurately defined because
of the absence of conodont faunas in the Caninia Dolomite. One sample (C 39) of
the Caninia Dolomite has yielded a fauna containing C. unicornis Youngquist &
Miller and M. beckmanni Bischoff. This indicates that at least the upper part of the
Caninia Dolomite is within this assemblage zone. The upper limit of the assemblage
zone coincides with the oldest stratigraphic occurrence of Taphrognathus varians
Branson & Mehl, which is found in the Upper S2 Subzone.

Remarks : This assemblage zone occupies the C2S1 Zone and the lower and
middle of the S2 Subzone (Samples C 39-S 44). Together with the overlying
Taphrognathus varians-Cavusgnathus- Apatognathus Assemblage Zone, it is equiva-
lent to the middle and upper part of Cu II S in Europe and to the Warsaw, Salem,
and lower part of the St. Louis Formation of North America.

The very small number of conodonts present in this stratigraphic interval precludes
a more detailed division, although the presence of G. cuneiformis Branson & Mehl at
the base of the assemblage zone may provide the basis for future correlation. The
overall aspect of the conodont faunas from this and the overlying conodont assembl-
age zone of the Avonian are similar to those described by Rexroad & Collinson (1963
and 1965) (see p. 61 for detailed discussion).

Taphrognathus varians — Cavusgnathus — Apatognathus Assemblage Zone

Characteristic species : T. varians Branson & Mehl, C. unicornis Youngquist
& Miller, and S. cristulus Youngquist & Miller.

Limits : The limits of this assemblage zone coincide with the stratigraphic range
of T. varians Branson & Mehl as at present known in the Avonian.

Remarks : This assemblage zone is present in the upper part of the S2 Subzone
of the Avonian (Samples S 45-S 58). It is tentatively correlated with the lower part
of the St. Louis Formation of North America. It is equivalent to the uppermost
Cu II 8 in Germany.

Specimens transitional between Cavusgnathus and Taphrognathus, which are

44 BRITISH AYONIAN CONODONT FAUNAS

identical to those from the St. Louis illustrated by Rexroad & Collinson (1963), have
been found in this assemblage zone.

Apatognathus geminus — Cavusgnathus Assemblage Zone

Characteristic species : Cavusgnathus spp. and Apatognathus geminus (Hinde).

Limits : The lower limit is marked by the last appearance of Taphrognathus
varians Branson & Mehl. The upper limit of the zone is marked by the first appear-
ance of Gnathodus bilineatus (Roundy).

Remarks : This assemblage zone occupies the Upper S2 and the Di Subzones
(Samples S 59-D 9) . No Di Subzone conodonts were recovered from the North Crop.
The assemblage zone is one of few conodonts, but is characterized by the presence of
the genera Apatognathus Branson & Mehl and Cavusgnathus Harris & Hollingsworth.
It is tentatively correlated with the Apatognathus geminus-Cavusgnathus Assemblage
Zone of North America, which is found in the upper part of the St. Louis Formation.
This is equivalent to the lowest part of Cu III a in Germany.

Sample D 10 which marks the first appearance of G. bilineatus (Roundy) is tenta-
tively taken as the basal sample of D2 although the D1-D2 boundary in the type
section is difficult to determine. One anomalous feature of this zone is the occurrence
of a fauna from the North of England associated with Bollandoceras hodderense (Bi).
This would generally be correlated with S2 of the Avonian (e.g. Thomas & Prentice
1965 : 43). This fauna includes M. bipluti Higgins with G. symmutatus sp. nov.,
G. girtyi simplex Dunn, G. commutatus Branson & Mehl), G. bilineatus (Roundy) and
G. homopunctatus Ziegler.

The subsequent assemblage zones were established from the D2 and D3 successions
on the North Crop. The few scattered conodonts of this age that were recovered
from the Avon Gorge show a general similarity to the North Crop faunas.

Mestognathus beckmanni — Gnathodus bilineatus Assemblage Zone

Characteristic species : Mestognathus beckmanni Bischoff, Cavusgnathus
unicornis Youngquist & Miller, Spathognathodus scitulus (Hinde), Apatognathus
bladus sp. nov., Hibbardella abnormis Branson & Mehl, Neoprioniodus montanaensis
(Scott), Gnathodus girtyi girtyi Hass, G. bilineatus (Roundy), and indeterminate
magnilaterellids.

Limits : The lower limit of the zone is tentatively taken as the first appearance
of G. bilineatus (Roundy), but the absence of conodonts in samples of Di North Crop
strata makes this position provisional. Further collecting will probably reveal an
earlier occurrence of this species, which is present in Cu III a of Germany. The top
of the zone is marked by the incoming of G. mononodosus sp. nov.

Remarks : This assemblage zone is represented by the lowest 60 ft. of the D2
Subzone of the North Crop (Samples CYD i-CYD 6). It is equivalent to part of the
Cu III a in Germany, and broadly equivalent to the St. Genevieve Formation of the
Mississippi Valley. The zone is no younger than the Pib Subzone of Northern
England.

BRITISH AVONIAN CONODONT FAUNAS 45

Gnathodus mononodosus Assemblage Zone

Characteristic species : Gnathodus girtyi simplex Dunn, G. girtyi girtyi Hass,
G. mononodosus sp. nov., G. bilineatus (Roundy), G. commutatus (Branson & Mehl),
G. homopunctatus Ziegler, and Spathognathodus cristulus Youngquist. Mestognathus
neddensis sp. nov. and M. bipluti Higgins are characteristic of this zone in the North
Crop.

Limits : The lower limit is marked by the first appearance of G. mononodosus sp.
nov. The upper limit is marked by the first appearance of Gnathodus girtyi collinsoni
subsp. nov. The latter subspecies has not yet been recorded from the Midlothian
section, however.

Remarks : This zone is represented by the highest 10 ft. of the D2 Subzone and
by the lowest 6 ft. of the D 3 Subzone (Samples CYD 7-3D 7) in the North Crop.
Our Yoredale samples have yielded no mestognathids. No mestognathids are
present in the Fife faunas and Collinson & Druce (in press) failed to recover them from
their Irish Visean fauna. We agree with their suggestion that the genus has an
irregular geographic distribution. It is not present in the prolific Upper Mississippi
Valley faunas of this age. The top of this zone in the Yoredales is the top of the
Simonstone Limestone (Pid). It is equivalent to the Cu III (3 of Germany and to
the late Valmeyran of the Upper Mississippi Valley.

Gnathodus girtyi collinsoni Assemblage Zone

Characteristic species : Gnathodus girtyi collinsoni subsp. nov., G. girtyi
simplex Dunn, G. girtyi girtyi Hass, G. nodosus Bischoff, G. mononodosus sp. nov., G.
bilineatus (Roundy). Prioniodina stipans (Rexroad) and P. subaequalis (Higgins)
are characteristic of the lower part of this zone in the North Crop and in Dunbar.
Neoprioniodus scitulus (Branson & Mehl), N. tulensis (Pander) and Ligonodina levis
(Branson & Mehl) are characteristic of the higher part in Scotland.

Limits : The lower limit is marked by the first appearance of G. girtyi collinsoni
subsp. nov. The upper limit is not defined in the present study.

Remarks : This zone is represented by the uppermost 18 ft. of the D 3 Subzone
of the North Crop (Samples 3D 8-3D 23). In the Yoredale section it is represented
by samples Y 29-Y 10 comprising the Middle Pi d , the Five Yard, the Three Yard
and the Underset Limestone (P2b-P2c)- The zone is equivalent to the Cu III y of
Germany and broadly equivalent to the Lower Chesterian of the Mississippi Valley.
It may be partly equivalent to the Lower Namurian, depending on where the upper
boundary is ultimately defined. G. girtyi turritus Collinson & Druce is known to
extend into the Namurian in Eire (Collinson & Druce in press). It is broadly
equivalent to the pre-Middle Glen Dean Chesterian faunas of North America.

The establishment of zonal limits in the upper part of the D succession was
difficult. The last appearance of Mestognathus beckmanni, Mestognathus bipluti,
Gnathodus homopunctatus, and the first appearance of Cavusgnathus naviculus,
Gnathodus nodosus and Gnathodus girtyi turritus were each in turn considered as

46 BRITISH AVONIAN CONODONT FAUNAS

possible markers for zonal limits, but the first appearance of Gnathodus girtyi
collinsoni subsp. nov. was the one in our opinion with the most widespread and
meaningful application.

Within a broad depositional basin there is a general similarity between the species
of " bar and blade " conodonts in each of the upper zones, but these similarities do
not extend to more distant areas, and we have therefore not listed them as character-
istic of the zones as a whole.

(d) Intra-Avonian correlation in Britain

(i) Avon Gorge — North Crop (Figs. 49-52).

There is a close overall similarity between the Lower K conodont faunas of both the
Avon Gorge and the North Crop (Fig. 14). The lowest beds of both are characterized
by the presence of Spathognathodus plumulus plumulus sp. et subsp. nov. and Patro-
gnathus variabilis gen. et sp. nov. The absence in the lowest beds of the North Crop
of Pseudopolygnathus vogesi sp. nov. which is present in the basal beds of the Avon
Gorge, probably implies a slightly older age for the North Crop strata. Siphonodella,
a most important diagnostic genus for the Carboniferous, and the Polygnathus
inornatus group first appear at comparable horizons in the North Crop and the Avon
Gorge. The last appearance of Siphonodella in both sections coincides with the first
appearance of Spathognathodus robustus, a species whose first appearance overlaps
the last appearance of the Polygnathus inornatus group.

In the Avon Gorge, Spathognathodus costatus costatus first appears just below the
traditionally accepted K-Z Zone boundary, whereas in the North Crop, it occurs just
above it. The general ranges of all these species are so similar in the two areas, that
correlation is relatively straightforward. Details are given on p. 36 in the zonal
discussion and in Fig. 14.

In spite of the overall lithological similarity between the Lower Z Zone strata in
both areas, there is a lack of any detailed resemblance in their platform conodont
faunas. We tentatively interpret this as the result of geographical isolation of
certain conodontifers (see p. 36). This probably reflects the influence of palaeo-
geographical factors, in spite of the fact that other studies have suggested a relatively
uniform depositional basin in this area during early Z times.

The incoming of Polygnathus lacinatus and of characteristic Pseudopolygnathus
multistriatus in the higher part of the Z Zone of both areas provides a firm basis for
correlation. The absence of Pseudopolygnathus cf. longiposticus in the North Crop
suggests that the higher part of the Z Zone is unrepresented there.

S2 and C2S1 rocks from the North Crop have yielded no conodonts, and Avon Gorge
faunas of this general age and also of the Di Subzone are also sparse. The presence of
Gnathodus bilineatus near the base of D2 in both areas re-establishes the correlation
in the higher part of the Avonian. Above this level, conodonts are so rare in the
Avon Gorge that no useful comparison can be made with the abundant faunas of
the North Crop.

BRITISH AVONIAN CONODONT FAUNAS

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48 BRITISH AVONIAN CONODONT FAUNAS

(ii) Farlow (Fig. 53).

The K Zone samples from Farlow (FAR 4A-7) yield a fauna broadly similar to that
of the lower strata of the Avon Gorge, and the North Crop, although there are some
differences. The lowest beds (FAR 4A) are characterized by the presence of both
Patrognathus variabilis gen. et sp. nov. and Polygnathus inornatus inornatus, together
with Clydagnathus gilwernensis gen. et sp. nov., and Polygnathus communis. The
first and third of these species occur together in the lowest zone of the Avonian (the
Patrognathus variabilis-Spathognathodus plumulus plumulus Zone) but Polygnathus
inornatus inornatus is confined to the overlying zone, where it occurs with P.
inornatus rostratus subsp. nov., which is found in the immediately overlying sample
at Farlow (FAR 4), and P. lobatus s.l. which is found in the next overlying sample
at Farlow (FAR 5). In the Avon Gorge, P. variabilis is associated with Poly-
gnathus inornatus in this zone. The lowest K Beds of Farlow thus appear younger
than those of the North Crop or the Avon Gorge. Furthermore, Sample FAR 5
also contains Spathognathodus cf. robustus, S. crassidentatus , 5. elongatus and S.
tridentatus, all of which are characteristic of the Spathognathodus cf. robustus-
Spathognathodus tridentatus Zone of the North Crop and Avon Gorge. It therefore
appears that the K Zone at Farlow represents a very condensed succession, the
overlying beds of the K Zone at Farlow yielding an almost identical fauna to that
of Sample FAR 5.

The Z Zone strata at Farlow are marked by the appearance of Spathognathodus cf .
cristulus and Ligonodina beata nom. nov. in the lowest beds (ORZ 1) and Spathog-
nathodus costatus costatus, and Clydagnathus darensis gen. et. sp. nov. in the overlying
beds (ORZ 2). These species are characteristic of the Spathognathodus costatus
costatus-Gnathodus delicatus Zone, as is Clydagnathus unicornis gen. et sp. nov.,
which occurs in the overlying beds (ORZ 3). A single specimen of Gnathodus
antetexanus in Sample ORZ A3, represents an anomalous faunal association, since
its first appearance in the Avon Gorge is in beds of Z2 age.

(iii) Yorkshire (Fig. 54).

A reconnaissance sampling programme of the Yoredale succession has yielded
abundant and well preserved conodont faunas characteristic of the higher Avonian
zones of the South Western Province. Although we have dissolved 7 kilogrammes
of the Hawes and Gayle Limestones, the beds have yielded no diagnostic conodonts.
The Hardraw Scar and Simonstone Limestones contain Gnathodus mononodosus sp.
nov. and G. homopunctatus and thus fall within the G. mononodosus Assemblage Zone.
The fauna of the overlying Middle Limestone is marked by the first appearance of
Gnathodus girtyi collinsoni subsp. nov., and the Five Yard Limestone is characterized
by the first appearance of G. girtyi turritus. These limestones therefore represent
the G. girtyi collinsoni Zone. Although Varker (1967) has suggested that species of
the genus Apatognathus may provide a useful basis for zonation and correlation in
the Yoredales, we have found the genus to be rare, rather than common, as he
claims, and we do not consider it useful in correlation.

BRITISH AVONIAN CONODONT FAUNAS

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50 BRITISH AVONIAN CONODONT FAUNAS

(iv) Scotland (Figs. 55-58).

Our general descriptions of Scottish faunas represent only a reconnaissance study,
our object being to discover whether or not our Avonian zones could be recognized
there, rather than to provide any comprehensive solution to the complex problems of
correlation of the Carboniferous of that area.

We have suggested a provisional application of our zonal scheme to Scotland (Fig.
15), but have made no precise correlations of individual limestones within particular
zones, although we believe this will later prove possible.

Dunbar

In Dunbar the Long Craig Upper Limestone, which was sampled at 6" intervals
(DUN 52-71) has a typical G. mononodosus Assemblage Zone fauna, which contains a
relatively large proportion of mestognathids. The general aspect of this fauna is
strongly reminiscent of the uppermost D2 Subzone of the North Crop. The over-
lying Skateraw Lower Limestone (DUN 72, 73) yields a typical G. girtyi collinsoni
Zone fauna although G. g. collinsoni subsp. nov. itself is present only in the higher of
two limestone samples. This may suggest that the limestone is transitional between
this and the underlying zone. The Skateraw Middle Limestone (DUN 74, 82) is
barren in its lowest sample, but the overlying sample (DUN 75) yields the first
specimens of G. girtyi turritus, a subspecies which first appears in the upper beds of
the D3 Subzone on the North Crop. This subspecies continues to be a characteristic
member of faunas of higher beds. The Barness East Limestone (DUN 87, 88),
although it has yielded only small faunas, is characterized by a very high proportion
of cavusgnathids, including both C. naviculus and C. convexus (Fig. 57).

Midlothian

Although the limestones of the Lower Limestone Group of Midlothian (NGL 1-17,
VEX 1, BIL 100-3) have provided no diagnostic species which enable us to correlate
them with a precise Avonian conodont zone, the overall aspect of their faunas is
strikingly similar to those of the D3 Subzone of the North Crop. The presence of
subspecies of G. girtyi and especially the first appearance of G. g. turritus in the
Vexhim Limestone are useful indications of the general age of these strata (Fig. 56).

The Gilmerton Limestone (GILM 1-7) was collected from the best available section
in Midlothian, but this was not the type locality, although we have included it in
Fig. 56 in the position of the type Gilmerton Limestone in the Lower Limestone
Group succession. It has a fauna of blades, which are more characteristic of higher
levels within the D3 sequence. We therefore suspect that the identification of the
limestone at a quarry one mile S.S.E. of Carlops as the Gilmerton Limestone, as given
in the Midlothian Coalfield Memoir (1958 : 20), is incorrect.

Fife

The Calciferous Sandstone Measures of Eastern Fife are characterized by relatively
few limestone bands in a thick succession of dominantly clastic strata and coals.

BRITISH AVONIAN CONODONT FAUNAS 51

Only three samples (ANS 15, 43, 388) have yielded any conodonts, and of these there
are few diagnostic species, although the presence of subspecies of G. girtyi indicates an
overall correlation with the D Zone of the North Crop (Fig. 55).

The Lower Limestone Group has yielded a small fauna from the Hurlet Limestone
(HURLET A, C, E) which is characterized by G. girtyi girtyi and G. girtyi simplex.
The Lower Hosie Limestone (HOSIE 1) yields a larger but essentially similar fauna,
but the Middle Hosie Limestone (HOSIE 2A-C) has yielded over 1,000 conodonts
and is characterized by G. girtyi collinsoni subsp. nov., as well as G. mononodosus
sp. nov. and G. nodosus, which suggests a correlation with a high level in the D3
Subzone of the North Crop.

Ayrshire

The Broadstone Limestone (BRAU 1-8) yielded a very meagre conodont fauna,
having an average yield of only one conodont per kilogram of rock. The fauna is
characteristic of the Cavusgnathus unicornis-Apatognathus Zone (Fig. 58).

The Dockra Limestone (BRAU 9 and 10) yields a large and well preserved conodont
fauna. G. girtyi simplex and G. girtyi girtyi each represent almost one third of the
total specimens in each sample studied. The presence of G. girtyi turritus at the base
of the Dockra Limestone shows this to be within the G.g. collinsoni Zone.

The Hosie Limestones from Glengarnock (GLEN 1-19) have yielded abundant
and well preserved conodont faunas, which include three specimens of G. g. turritus,
which is indicative of the G.g. collinsoni Zone.

The Index Limestone (DR IN i-GO IN 3) of Ayrshire has yielded faunas which are
dominated by Gnathodus girtyi girtyi, G. girtyi simplex and G. girtyi collinsoni
subsp. nov., as well as other species characteristic of the Gnathodus girtyi collinsoni
Zone of the North Crop.

The Lower Linn Spout Limestone (LINL, 1, 3) has yielded only five conodont
specimens. These include G. girtyi girtyi, Mestognathus sp. and Magnilaterella sp.
which in themselves are not diagnostic.

The Upper Linn Spout (U.LIN 1-7) has a small fauna which includes G. bilineatus,
G. mononodosus sp. nov., G. nodosus and G. commutatus.

We can make no precise correlation of this formation, but, clearly, the presence of
some 300 ft. of underlying strata within the G. girtyi collinsoni Zone of Ayrshire
implies a relatively young age. We have assigned the Upper Limestone Group to the
Eumorphoceras Zone on the basis of Currie's (1954 : 535) goniatite faunas from the
Index Limestone.

Roxburghshire
The main Algal " Series " of Garwood in Harden Burn yielded abundant and well
preserved conodont faunas. These were dominated by the Polygnathus lacinatus
group and other species including Cavusgnathus cristatus and Taphrognathus varians.
In spite of some differences between this fauna and those of the Avon Gorge, the
presence of polygnathids shows the Roxburghshire faunas to be equivalent to the
early C Beds of the Avon Gorge. This accords well with the tentative Ci age
assigned to these beds by Garwood (1931).

52 BRITISH AVONIAN CONODONT FAUNAS

Summary

Our overall Scottish correlations show a very close similarity to those proposed by
Currie (1954, Table 1) on the basis of her goniatite studies. The only difference
involves the first appearance of G. girtyi collinsoni subsp. nov. in the Middle Hosie
Limestone of Fife.

On the basis of this we have proposed the tentative correlation shown in Fig. 15,
but it seems probable that the absence of this subspecies from underlying strata is
the result of the relatively poor yields of the Lower Hosie (29 individual conodonts)
and Hurlet Limestones (15 conodonts).

This diagnostic subspecies is represented by less than 3 % of the total fauna of each
of the two overlying Middle Hosie samples, each of which comprises more than 400
identifiable conodonts.

(e) Correlation of the Avonian with Europe and North America

The purpose of this section is to discuss the value of conodonts in the correlation
of the British type Avonian section with type sections in North America and Western
Europe. The sections in the Mississippi Valley, the conodont faunas of which were
described by Collinson, Scott & Rexroad (1962), are taken as standard sections for
North America, and the West German Lower Carboniferous sections, the conodont
faunas of which were described by Bischoff (1957) and Voges (1959), are taken as
standard sections for Western Europe. We have also made provisional correlations
with the Franco-Belgian Tournaisian Vis£an succession, basing our comparisons on
the faunas reported, but not described, by Conil, Lys and Mauvier (1964).

The general results of this correlation are most gratifying. We have been able to
suggest the relative equivalence of most of the various divisions of the North
American, German, French, Belgian and British successions with a sufficient degree
of confidence and precision to provide a satisfactory overall stratigraphic control.
In those cases where our correlation is more tentative, we have discussed the limits of
uncertainty, and these are seldom great. We have had the great advantage of
working in virtually continuous Avonian rock sections, and some of the present
anomalies between our faunal successions and those of other areas, such as Germany,
and, to a lesser extent, the Mississippi Valley, probably lie in the scattered outcrops
on which the latter are based. More information is needed from all areas before the
present faunal similarities and differences can be fully interpreted.

(i) North America and West Germany

The K and Z Zones oj the Avonian.

The K and Z Zones of the Avonian are, in many respects, the most difficult part
of the succession to correlate with other areas, largely because of the absence from
them of some zonal species, and the presence of new genera and species which are,
at present, not known with certainty from other areas.

An important element of the K Zone fauna is the group of new species, which are
confined to that zone ; these include Patrognathus variabilis gen. et sp. nov., Clyda-

BRITISH AVONIAN CONODONT FAUNAS 53

gnathus gen. nov. and Spathognathodus plumulus plumulus sp. nov. Although these
species are new, they show some resemblances to specimens described from other
areas.

Klapper & Glenister (1966) have described faunas from the Canning Basin of
Western Australia. Their " ? Scaphignathus velifera " is, according to Dr. Klapper
(personal communication), probably congeneric with Clydagnathus, having a large
basal cavity, which removes it from Scaphignathus. This species occurs in two
samples. In one of these, it is not associated with other conodonts, and lies strati-
graphically about 150 ft. below Spathognathodus aculeatus. In the other, it occurs
with that species and with Palmatolepis glabra subsp. indet. It is clearly, therefore,
of Upper Devonian age in this area. This does not necessarily imply an Upper
Devonian age for the K Zone of the Avonian, however. The resemblance of the
Australian specimens to those from the K Zone is not exact, and they may represent
distinct species. The association of the Australian specimens with 5. aculeatus
implies an age within the costatus Zone and the Tni a of Belgium, but the absence of
S. aculeatus in the Avonian K Zone conodont faunas suggests that they are of younger
age.

The presence of Spathognathodus costatus in the K Zone of the Avonian could imply
an Upper Devonian age, but 5. costatus, as we have now defined it, differs from S.
costatus of German authors. The relative position of other Avonian genera makes a
Carboniferous age even more probable. Our S. costatus is confined to beds in the
Avonian lying above both Siphonodella and our single specimen of Elictognathus.
Furthermore, the gnathodids, although they first occur 150 ft. above the position of
5. costatus in the Avon Gorge, are advanced species which are of undoubted Carboni-
ferous age in other areas. The earlier species of Gnathodus (G. kockeli etc.) are not
represented in the Avonian faunas.

Bouckaert & Ziegler (1965) have described a Fammenian conodont fauna from
Belgium, in which are found five specimens of Scaphignathus veliferus (1965, PI. 5,
figs. 5-7) in a sample from the Montfort section at Esneux. These specimens
probably represent the genus Clydagnathus, although they do not appear conspecific
with forms from the K Zone.

The genus Palmatolepis is characteristic of the Upper Devonian but Bischoff (1957)
and Voges (1959) have reported Palmatolepis in the basal Cu I beds of West Germany.
In North America, in the Mississippi Valley, Palmatolepis is abundant in the Saverton
Shale, common to rare in the Louisiana Limestone and occurs rarely in the basal
beds of the Hannibal. Collinson (1961) stated that " the occurrence of Palmatolepis
glabra and Palmatolepis gracilis in the European Lower Carboniferous, as well as in
the Mississippi Valley Hannibal Formation, may represent stratigraphic admixture,
but it seems more likely that they are indigenous ". Specimens of the vast majority
of Upper Devonian faunas yield abundant Palmatolepis, and the absence of palmato-
lepids in the Avon Gorge provides some negative evidence in support of the assign-
ment of the lowermost strata to the Carboniferous.

Fewer than 2 % (Klapper & Furnish, 1962 : Ziegler 1962, table 7 : Bouckaert &
Ziegler 1965, Chart 9) of the Upper Devonian faunas described lack Palmatolepis, and

54 BRITISH AVONIAN CONODONT FAUNAS

the genus is present in Devonian faunas in southwestern England. We stress that
these are negative data, however ; indeed, it seems possible that a few Lower
Carboniferous faunules may contain indigenous palmatolepids.

It is possible that our Lower K faunas are close to the fauna briefly described by
Bouckaert & Ziegler (1965, Chart 9, p. 25) from the section at Huy 2 in Belgium.
The highest part of this section (19) contains a new genus (not described, illustrated,
or mentioned in the text) together with S. aculeatus E. R. Branson and Pseudopoly-
gnathus dentilineatus E. R. Branson. The first of these two species may represent
S. plumulus. Bouckaert & Ziegler also record from the same sample (1965 : 17), a
single specimen of a form " which seems to represent a new trend evolved from
Spathognathodus costatus " (PI. 4, fig. 12 and p. 27 : Pseudopolygnathus sp.). This is
close to our Pseudopolygnathus vogesi sp. nov. A Lower Tournaisian age for this
part of the Belgian section has been suggested by Conil (1964) on the basis of the
foraminifera, and Streel (1966) states that the spores indicate a Devonian age.

Klapper & Sandberg (1967 : B 52) have found the genus Patrognathus in a very
thin interval of strata in Wyoming (the Windy Gap Formation). It is associated
with Siphonodella sulcata, a species that was also recovered by these authors from
the upper part of the G. kockeli-P. dentilineatus conodont zone in Germany (Voges
1959, text-fig. 1, Samples 3 and 4).

An undescribed conodont fauna from the Lower Pilton Beds contains Spatho-
gnathodus plumulus sp. nov., Pseudopolygnathus vogesi sp. nov. and representatives of
the genus Clydagnathus (J. W. Williams, personal communication) . The Lower Pilton
Beds are considered to be of Wocklumeria age (Goldring 1955). However, no speci-
mens of the genus Patrognathus have as yet been found in the Lower Pilton Beds.
Thus the Lower Limestone Shale appears to be younger than the Lower Pilton Beds.
The conodont fauna of the Lower Pilton Beds is unlike the fauna from the Wock-
lumeria to VI Zone described by Ziegler (1962). It is closer to the fauna described
by Bouckaert & Ziegler (1965), from the uppermost Fammenian at Huy.

All the evidence points to the conclusion that a gap in the conodont sequence is
present in the type section of the Devonian-Carboniferous boundary in the Honnetal
railway cutting. The Huy section of Fammenian age is younger than the type to VI
strata at Honnetal, but on goniatite and spore evidence it is still Devonian. The
base of the Lower Limestone Shale is younger than the Huy section (on the basis of
the absence of the genus Patrognathus in the Huy section), but is older than the base
of the Tournaisian in the Honnetal railway cutting.

Thirty feet above the base of the K section in the North Crop a single specimen of
Elictognathus has been found. Elictognathus makes its first appearance in North
America at the base of the Siphonodella sulcata Assemblage Zone which is near the
the base of the Hannibal Formation, and is correlated with the middle part of the
Lower Carboniferous Cu I Zone of Western Europe (Collinson, Scott & Rexroad
1962).

Associated with Elictognathus in the Pseudopolygnathus vogesi-Clydagnathus
Assemblage Subzone of the Avonian is Pseudopolygnathus vogesi sp. nov. This
species is characteristic of the lower part of the Lower Carboniferous Cu I Zone of

BRITISH AVONIAN CONODONT FAUNAS 55

Western Europe (Voges 1959). Collinson, Scott & Rexroad (1962) noted that the
first appearance of the genus Pseudopolygnathus in the Mississippi Valley was at
the base of their Gnathodus n. sp. B.-Gnathodus kockeli Assemblage Zone, which is
confined to the Glen Park and the basal Hannibal Formations and is correlated
with the lowermost part of the Lower Carboniferous Cu I Zone of Western Europe.
The upper part of the Pseudopolygnathus vogesi-Clydagnathus Assemblage
Subzone has specimens of P. inornatus which Ziegler (1962), who referred to
them as Polygnathus nodomarginatus, found in the Middle and Upper Spathognathus
costatus Zones, as well as in the G. kockeli-P. dentilineatus Zone. Dr. C. W.
Collinson (personal communication) has found similar specimens in the Mississippi
Valley, where they appear to be forerunners of Siphonodella sulcata. These are
found in abundance, and are associated with Gnathodus kockeli in the base of the
Hannibal Formation at several localities (just below the lowermost Siphonodella
Zone).

The conodont fauna of the K and basal Z Zones of the Avonian is also difficult to
correlate precisely with the American and West German successions, because of the
rarity of the genus Siphonodella in the K Zone and its absence in the Z Zone. This
genus is one of the most useful of all guide fossils in other areas, where individual
species are distinctive, short ranging, and have a wide geographical distribution
(Collinson, Scott & Rexroad 1962, Chart 2). In North America and West Germany
ranges of individual species have been used to define the boundaries of conodont
assemblage zones.

In the Avonian, the genus Siphonodella is confined to the Siphonodella-Polygnathus
inornatus Assemblage Zone. Specimens from the Avon Gorge, although fractured,
have rostral ridges and are more advanced in development than Siphonodella sulcata,
the earliest known species in North America, where it occurs near, but not at, the
base of the Hannibal Formation. Specimens from the North Crop are identified as
Siphonodella isosticha. This species in North America ranges from the base of the
Upper Hannibal Formation to the top of the Upper Chouteau Formation. Thus the
base of our Siphonodella-Polygnathus inornatus Assemblage Zone cannot be older
than the base of the upper part of the Hannibal Formation, which is included in the
lower part of the Siphonodella quadruplicata-Siphonodella crenulata Assemblage Zone
of the Mississippi Valley.

Correlation of the base of this zone with our Siphonodella-Polygnathus inornatus
Assemblage Zone, would make it broadly equivalent to the lower part of the Cu II a
Zone of the European Lower Carboniferous. This is supported, to some extent, by a
consideration of the ranges of gnathodid species, which provide a possible correlation
for the higher part of the Avonian section.

Klapper (1966) has described a fauna from the Lodgepole Limestone of Montana
and Wyoming, which is referable to the Lower Siphonodella crenulata Zone (Cu II a)
of Germany and from the Mississippian part of the Dark Shale Unit, which is referable
to the Siphonodella-P . triangulus triangulus Zone (Cu I). These faunas are in part
similar to the Upper K Zone fauna of the Avonian.

The conodont fauna of the Spathognathodus robustus-Spathognathodus tridentatus

5 6 BRITISH AVONIAN CONODONT FAUNAS

Assemblage Zone is similar to that described by Branson & Mehl (1934A) from the
Bushberg Sandstone of Missouri, while the fauna of the basal Spathognathodus
costatus sulci ferus-Gnathodus delicatus Assemblage Zone is similar to that of the
Hannibal Formation of Missouri described by E. R. Branson (1934).

Our faunas from the K and Z Zones seem to agree closely with those described by
Branson & Mehl (1934A) from the Bushberg, E.R.Branson (1934) from the Hannibal,
and Cooper (1939) from the pre-Welden Shale Formations. This suggests that the
biostratigraphic zones set up by Collinson, Scott & Rexroad (1962) may not be fully
representative of the conodont faunas of the lowermost Lower Carboniferous of the
whole of North America, as opposed to the Illinois Basin. Further work on Missouri
and Oklahoma sections would probably prove useful in correlation between North
America and the South West Province of Great Britain.

Gnathodus delicatus makes its first appearance in the Avonian 34 ft. (Sample ZLA 6
North Crop) from the top of the Spathognathodus costatus costatus-Gnathodus delicatus
Assemblage Zone. In North America this species first appears at the base of the
Chouteau Formation, in the top of the Siphonodella quadruplicata-Siphonodella
crenulata Assemblage Zone, but little is known about the distribution of Upper
Hannibal gnathodids, and it is therefore possible that Gnathodus delicatus may
appear lower in the section. The top of the Hannibal Formation is the zone of few
gnathodids of Collinson, Scott & Rexroad (1962). A similar zone of few gnathodids
is also present in Germany. Branson & Mehl (1938A : 136) remarked that the
Chouteau conodont assemblage is characterized by the introduction of Gnathodus.
The base of the Chouteau Formation also corresponds to the oldest stratigraphical
occurrence of the upper zone of Gnathodus shown by Collinson, Scott & Rexroad
(1962, Chart 3).

The earliest occurrence of Gnathodus delicatus in the Avon Gorge, which is some-
what higher (base Sample Z 29) in the section than the earliest occurrence on the
North Crop, is represented by relatively large numbers of specimens, in contrast to the
few specimens found in its first occurrence on the North Crop. The earliest occur-
rence of Gnathodus delicatus on the North Crop may be correlated to the Siphonodella
quadruplicata-Siphonodella crenulata Assemblage Zone occurrence of North America,
which lies within the Zone of few gnathodids, whereas the Avon Gorge first occurrence
may be correlated with the abundant occurrence of Gnathodus delicatus in North
America, near the upper limit of the Siphonodella isosticha-Siphono delta cooperi
Assemblage Zone, which occupies the upper part of the Chouteau Formation and is
correlated with the upper part of the European Lower Carboniferous Cu II a Zone.

Rexroad & Scott (1964) described the conodont faunas from the Siphonodella
isosticha-Siphonodella cooperi, Gnathodus semiglaber-Pseudopolygnathus multistriatus,
Bactrognathus-Polygnathus communis and Bactrognathus-T aphrognathus Assemblage
Zones, when they described the conodont fauna of the Rockford Limestone and New
Providence Shale. They noted (Table 2 : 15) that Gnathodus delicatus was most
abundant in the Siphonodella isosticha-Siphonodella cooperi Assemblage Zone,
Gnathodus semiglaber most abundant in the overlying Gnathodus semiglaber-Pseudo-
polygnathus multistriatus Assemblage Zone and Gnathodus antetexanus most

BRITISH AVONIAN CONODONT FAUNAS 57

abundant in the overlying Bactrognathus-Polygnathus communis Assemblage Zone.

In the Avonian of the Avon Gorge a similar change in the gnathodid fauna is seen.
Gnathodus delicatus occurs near the base of the Z2 Subzone, Gnathodus semiglaber is
present in the upper part of Z2 and Gnathodus antetexanus first appears in the upper
part of Z2 and ranges into the lower part of Ci (Fig. n).

The occurrence of gnathodids in Germany provides conflicting data for comparison.
Ziegler (i960, 1963) has described gnathodids identical to those of the middle Poly-
gnathus lacinatus Zone of the Avonian (Samples Z 28-Z 30). One of his faunules of
anchoralis age (i960) also contained Siphonodella and Mestognathus, but the other
yielded no representatives of Siphonodella. The anchoralis fauna of Germany, as at
present understood, contains the simultaneous first appearance of several species of
Gnathodus, which appear at different horizons in the Lower Carboniferous of Britain
and North America. We interpret this as partly the result of Bischoff & Voges'
limited stratigraphic sections and partly the result of the more recent taxonomic
refinements, which would now require the revision of the earlier specific nomenclature
of these authors.

Specimens referable to G. semiglaber, G. typicus, G. antetexanus and G. girtyi all
first appear at the base of the anchoralis Zone. It appears that the anchoralis Zone
as presently defined in Germany occupies a greater period of time than hitherto
thought and that the Cu II (3-y with which it is generally equated could include the
time interval Upper Z2-Upper C2 in the Avonian and at least from the top of the
Chouteau Formation to the top of the Burlington Formation in North America.

If the first appearance of species is used as the basis of correlation, the oldest
occurrence of Gnathodus delicatus in the Avonian is in the Spathognathodus costatus
costatus-Gnathodus delicatus Zone. In North America it first occurs in the Siphono-
della isosticha-S. cooperi Zone, which might thus be interpreted as being equivalent
to the Avonian Zone. This would make it equivalent to the Upper Chouteau, and
to the upper part of Cu II a of the German succession (Figs. 12, 16). Collinson,
Rexroad & Scott (1962) noted that the top of the Siphonodella isosticha-Siphonodella
cooperi Assemblage Zone was marked by a major unconformity in the Mississippi
Valley and was a cut-off horizon for Gnathodus delicatus. This is one possible
correlation, but the rarity of siphonodellids in the Avonian makes any such correla-
tion based on " first appearances " of species tenuous, and other aspects of the fauna
suggest a somewhat younger (Chouteau) age for the Avonian Zone.

The Siphonodella-Polygnathus inornatus Zone is also characterized by the presence
of Polygnathus inornatus s.l. and Siphonodella isosticha, both of which are character-
istic species of the Siphonodella isosticha-S. cooperi Zone of the Mississippi Valley
(Collinson, Scott & Rexroad 1962 : 21). Correlation of these two zones would thus
appear an alternative valid solution to the problem, the general absence of earlier
transitional siphonodellids in the Avonian being interpreted as a result of geographic
faunal variation, either in the absence of whatever conodont-bearing group they
represented, or, more probably, their " local " functional replacement by broadly
homologous polygnathids (Fig. 16).

Such a possible correlation is supported by the fact that in the Bonaparte Gulf of

BRITISH AVONIAN CONODONT FAUNAS

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Australia one of us (in Jones & Druce 1966) has recently discovered a series of
abundant conodont faunas extending through some 3,000 ft. of Lower Carboniferous
strata. There is a striking resemblance between the Australian and the Avonian
conodont successions, and although Siphonodella is abundant in the Australian
faunas, it does not extend up as high as the Spathognathodus costatus group (Fig.
16). This could mean that all the Siphonodella zones of the Mississippi Valley lie
below the first occurrence of 5. costatus in the Avonian, and would therefore be of K
age.

The other implication of such a correlation would be that the North American and
the German successions are more incomplete than has formerly been supposed, for it
would be difficult to find any North American equivalent of the two overlying
Avonian assemblage zones, if the correlation of the Avonian Polygnathus lacinatus
Zone and the Mississippian Gnathodus semiglaber-Pseudopolygnathus multistriatus
Zone (which seems to us to be very well established, p. 57) is accepted. This would
suggest that the unconformity known to exist beneath the Sedalia Formation of the
Mississippi Valley, is of greater magnitude than is generally assumed.

There may not be such a break in the Oklahoma or parts of the Missouri successions
(Cooper 1939 ; Branson & Mehl 1934A : 265). The Rockford Limestone fauna
(Rexroad & Scott 1964) reveals an apparent transition in northern Indiana from the
Siphonodella isosticha-S. cooperi Zone into the Gnathodus semiglaber-Pseudopoly-
gnathus multistriatus Zone, however, and represents an anomaly if the present
correlation is accepted, although most of the sections come from cores. There is,
however, an unconformity in southern Indiana between the Rockford and the over-
lying New Providence Shale. Even in areas of apparent transition of the two
assemblage zones within the Rockford Limestone, the faunal transition is abrupt
(Rexroad & Scott 1964, Table 1). Rexroad & Scott (1964 : 16-17) have written
" Although a number of species are common . . . this break between the Kinderhook
and Osage Series is unusually well marked. The faunal break is sharp, but a number
of species confined to the lower zone gradually decrease in number upward. Thus an
unconformity within the Rockford at the Kinderhook-Osage boundary is not
necessarily indicated. At the type section near Rockford (locality 10) the formation
is exposed only in the bed of the East Fork of White River, and even at low water the
evidence relating to a possible unconformity cannot be interpreted."

It may also be that the overlap of the Siphonodella and anchoralis faunas in
Germany implies a stratigraphic break between them, in which case part of the
Upper Cu II a and Lower Cu II (3 could be unrepresented. One of the major problems
concerning the anchoralis fauna is its patchy geographic distribution (p. 65). It is
possible that its limited distribution in North America (it is recorded from the
Pierson Formation of Missouri and the " Sedalia " of Illinois, above the uncon-
formity) may mean that in places it is represented by the unconformity which we
have postulated.

This alternative correlation has stressed the inadequate numbers of siphonodellids
in British Lower Carboniferous faunas, and its weakest point is the lack of a more
detailed series of species of this genus in the Avonian. The first provisional correla-

60 BRITISH AVONIAN CONODONT FAUNAS

lation, in which the ranges of gnathodid species were compared, is also limited by a
comparable, tantalizing " zone of few gnathodids " in the Middle and Upper
Hannibal of North America, and if, as we believe, both correlations are equally
reasonable, they are also equally vulnerable, because of a comparable lack of
detailed phylogenetic development in Britain and the United States.

The present available data are insufficient to allow us to make a final choice
between the two alternative correlations ; although we have shown the second on
our main correlation table (Fig. 12), we have summarized the evidence for both
on Fig. 16). The total stratigraphic differences involved between them are not
great, and it is perhaps a paradoxically satisfying aspect of the precision which we
believe conodonts offer, that we should be dissatisfied with an uncertainty of some
80 ft. in such a transatlantic correlation.

A new conodont fauna associated with the goniatites Protocanites and Muen-
steroceras from the Berwick Formation of Australia (Dr H. T. B. Jenkins, personal
communication) contains a fauna which is similar to the Z Zone fauna of the Avonian
in many respects. The pseudopolygnathids are identical to Zi and Lower Z2 speci-
mens. Associated with the pseudopolygnathids are many gnathodids, most of which
are new species, although a few are similar to G. punctatus, a species characteristic of
the upper part of Z2. Two specimens of Bactrognathus also occur in the Australian
fauna, suggesting that Bactrognathus is older than has hitherto been thought likely.

The fauna of Samples Z 31 to Z 38 with Gnathodus semiglaber and Pseudopoly-
gnathus multistriatus is similar to that of the Gnathodus semiglaber-Pseudopoly-
gnathus multistriatus Assemblage Zone of the Mississippi Valley. This Assemblage
Zone coincides with the " Sedalia " Formation of the Mississippi Valley and has been
correlated with the lowermost part of the Cu II (3 Zone of Western Europe. Dr W.
Ziegler (personal communication) believes that the gnathodid fauna of Samples
Z 34-Z 38 is identical to that found in Western Europe in beds equivalent to the
Siphonodella crenulata Zone (Voges 1959) and thus of Cu II a age.

C Zone.

In the upper part of the Z Zone and in the lower part of the Laminosa Dolomite,
Gnathodus antetexanus has been found, associated with Pseudopolygnathus cf.
triangulus triangulus, Polygnathus communis and Polygnathus lacinatus. The lower
limit of the Bactrognathus-Polygnathus communis Assemblage Zone in the Mississippi
Valley coincides with the earliest abundance of Gnathodus antetexanus, and the upper
with the youngest stratigraphical occurrence of Polygnathus communis. In the
Avonian of the Avon Gorge, the youngest stratigraphical occurrence of Polygnathus
communis is in the middle of the Laminosa Dolomite (the base of Sample C 10).
The Bactrognathus-Polygnathus communis Assemblage Zone is characterized by the
presence of Polygnathus communis, Pseudopolygnathus multistriatus, Pseudopoly-
gnathus triangulus pinnatus and by being the zone of abundant Gnathodus ante-
texanus. Samples Z 38-C 9 are correlated with this Assemblage Zone. In North
America, the zone extends from the base of the Fern Glen Formation to the top of

BRITISH AVONIAN CONODONT FAUNAS 61

the Middle Burlington Formation. In Western Europe it ranges from upper Cu II (3
into lower Cu II y.

In West Germany Bischoff (1957) recorded the first appearance of Mestognathus
beckmanni at the base of Cu III a, but Voges (1959) found a single specimen near the
base of Cu II (3/y. Kronberg, Pilger, Scherp and Ziegler (i960) also found Mesto-
gnathus beckmanni in beds of Cu II (3/y age. Meischner (1962) in his chart of strati-
graphic ranges (p. 31, fig. 10) showed the stratigraphic range of Mestognathus
beckmanni as commencing at the base of Cu II (3/y. The lowest occurrence of M.
beckmanni in the Avonian is in the upper part of the Laminosa Dolomite (the base of
Sample C 15). Thus the upper part of the Laminosa Dolomite appears to be of
Cu II p/y age.

In North America the base of the Bactrognathus-Taphrognathus Assemblage Zone
is marked by the highest occurrence of Polygnathus communis, and the top by the
lowest abundant occurrence of Gnathodus texanus, which makes its first appearance
near the top of the zone. The youngest stratigraphic occurrence of Polygnathus
communis in the Avonian is in the middle of the Laminosa Dolomite. It is con-
sidered that the middle of the Laminosa Dolomite, above the youngest occurrence of
Polygnathus communis (base Sample C 10), corresponds to the base of the Bactro-
gnathus-Taphrognathus Assemblage Zone of North America. In North America this
zone is confined to the upper part of the Burlington Formation and is correlated by
Collinson, Scott & Rexroad (1962) with the upper part of the European Cu II (3/y
Zone. Since Mestognathus has not been recorded from North America, our inter-
mediate faunas provide important confirmation of this correlation.

The Caninia Oolite in the Avon Gorge is characterized by the presence of two
species, Polygnathus bischoffi sp. nov. and Mestognathus beckmanni. In Western
Europe the youngest stratigraphic occurrence of Polygnathus bischoffi sp. nov. is at
the top of Cu II p/y. Gnathodus texanus s.s. occurs with Mestognathus beckmanni and
Polygnathus bischoffi sp. nov. in the Caninia Oolite of Fall Bay, Gower. Since the
youngest occurrence of Gnathodus texanus s.s. in North America is near the top of the
Bactrognathus-Taphrognathus Assemblage Zone, the upper part of the Laminosa
Dolomite and the Caninia Oolite are correlated with the Taphrognathus-Bactro-
gnathus Assemblage Zone and with the upper part of the European Cu II (3/y Zones.

A conodont fauna from Askeaton, Eire, contains specimens of G. texanus, P.
triangulus pinnatus and G. girtyi. The specimens of G. girtyi are identical to those
illustrated by Hass (1953) and clearly have developed from G. texanus. The
Askeaton fauna is therefore younger than the Caninia Oolite fauna and is best
correlated with the Caninia Dolomite.

S and D Zones.

The Cavusgnathus unicornis-Apatognathus libratus and the Taphrognathus varians-
Cavusgnathus-Apatognathus Zones of the Avonian cannot be precisely correlated
with the American assemblage zones. Although they have elements in common
with both the Taphrognathus varians-Apatognathus and the Apatognathus? geminus-
Cavusgnathus Assemblage Zones of the Mississippi Valley, there are also important

62 BRITISH AVONIAN CONODONT FAUNAS

differences between the two faunal successions. The Taphrognathus varians-
Apatognathus Assemblage Zone includes the Warsaw, Salem and the lower part of the
St. Louis Formations, and it is probably equivalent to the upper part of the Cu II 8
Zone of Western Europe. The limits of this assemblage zone were defined by
Collinson, Scott & Rexroad (1962) as follows : " The lower limit is marked by the
lowermost occurrence of Apatognathus? in the Valmeyeran Series plus the highest
occurrence of common Taphrognathus varians. The upper limit is distinguished by
the lowermost occurrence of Cavusgnathus and the youngest occurrence of Taphro-
gnathus as well as by the lower limit of the upper zone of abundant Apatognathus ".

The lowest stratigraphic occurrence in the Avonian of specimens identical to the
apatognathids illustrated by Rexroad & Collinson (1963) is near the base of Ci.
Taphrognathus does not appear in the Avonian until the upper part of the S Zone,
well above the first appearance of Cavusgnathus. Specimens transitional between
Cavusgnathus and Taphrognathus, identical to those illustrated by Rexroad and
Collinson from the boundary between the lower and upper St. Louis Formation, are
found in Samples S 49 to S 58 of the Avonian. Cavusgnathus first appears in the
Avonian in the middle of the Caninia Dolomite, well above the first appearance of
Apatognathus, and well below the first appearance of Taphrognathus. In North
America, however, the first appearance of Cavusgnathus is above the first appearance
of Taphrognathus and Apatognathus.

In the Scottish conodont faunas, Taphrognathus varians occurs with Polygnathus
lacinatus, a species which in the Avonian is common in the upper part of Z2 and in the
C Zone. Thus it would appear that the lowest occurrence of Taphrognathus in
Britain may be considerably lower than that noted from the Avonian of the South
West Province and it would then correspond more closely with the North American
occurrence.

The Apatognathus geminus-Cavusgnathus Assemblage Zone (Upper S2-Di of the
Avon Gorge) is equivalent to the upper part of the St. Louis Formation of the
Mississippi Valley and to the basal Cu III a of Germany.

In Germany, Mestognathus beckmanni ranges from the base of Cu II (3/y (and may
extend into Cu II a) to the middle of Cu III y (Bischoff 1957) although Meischner
(1962) gives the upper limit as Middle Cu III (3. Gnathodus bilineatus is present in
the Cu III and E Zones of Germany and Britain (Collinson & Druce in press : Higgins
1961), and G. girtyi girtyi ranges from Cu II y into the Namurian (Bischoff 1957),
although Meischner (G. girtyi Form A = G. girtyi girtyi) restricts it to the Cu III a
Zone, with the possibilities of homeomorphic development throughout Cu III. In
view of Bouckaert & Higgins' (1963) record of the species from the E2a of the Belgian
Dinant Basin and its presence in Pi and P2 of the Yoredale succession, the German
ranges cannot be used as the basis of correlation. The absence of the gnathodids,
G. semiglaber and G. texanus, as well as species of the genus Polygnathus, from this
Lower D2 Subzone indicates that it is younger than Cu II y.

Meischner (1962 : 31) has shown that G. girtyi simplex (G. girtyi Form B of
Meischner) first occurs very near the base of Cu III (3, while G. homopunctatus
occurs just below the base of Cu III (3. Thus the upper boundary of the Mestog-

BRITISH AVONIAN CONODONT FAUNAS 63

nathus beckmanni-Gnathodus bilineatus Zone appears to be at the base of the Cu III (3
Zone, the zone being confined to Cu III a.

The fauna resembles that of the St. Louis Limestone, and has a very close similarity
to that of the overlying St. Genevieve Formation.

The base of D2 in the Avonian is within the Gnathodus bilineatus-Cavusgnathus
charactus Assemblage Zone of North America. G. bilineatus first appears in the base
of this zone in the Mississippi Valley, but the details of this North American zone are
not yet fully studied (Collinson, Scott & Rexroad 1962 : 25). The species first
appears in the higher part (Unit C) of the Pella Formation of Iowa (Rexroad &
Furnish 1964).

One anomalous aspect of this correlation is the reported first appearance of the
Gnathodus girtyi group at the top of this zone in the Mississippi Valley (Collinson,
Scott & Rexroad 1962 : 25).

The Gnathodus mononodosus Zone includes the last appearance of M. beckmanni,
which is last found in the Middle Cu III (3 of Germany (Meischner 1962). The fact
that our zone is established on the basis of a new species makes more precise correla-
tion difficult. G. nodosus, which first appears at the base of this zone in the North
Crop, first appears in the Middle Cu III (3 zone of Germany (Meischner 1962).

The overlying Gnathodus girtyi collinsoni Zone represents the first appearance of
G. girtyi collinsoni (= G. girtyi Form C of Meischner 1962), which first appears at the
base of Cu III y, in the Middle Rhenaer Kalk of Germany. The last appearance of G.
homopunctatus on the North Crop falls within this zone, and this is closely similar to
its last appearance in Germany (Meischner 1962 : 31, Chart 10). The overall aspect
of this Avonian Zone is similar to that of the pre-Middle Glen Dean Chesterian
Formations of the Mississippi Valley.

(ii) France and Belgium

There are no adequately illustrated accounts of the Lower Carboniferous faunas of
France or Belgium, and our comparisons are made on the basis of published faunal
lists. We have not been able to study the original specimens, and our correlations
are, therefore, tentative and provisional.

Conil, Lys & Mauvier (1964) have studied the conodont faunas of the Tournaisian
and Visean in Belgium and France. They showed that Taphrognathus (synonymous
with Patrognathus gen. nov. or Clydagnathus gen. nov.) occurs in beds that are of
Tni a -Tn2b age. Associated with Taphrognathus in Tni b are Polygnathus inor-
natus, Pseudopolygnathus dentilineatus, Elictognathus costatus and Siphonodella
obsoleta, a fauna which is closely similar to that of the Upper K Zone. In Tn2b
Siphonodella duplicata, Siphonodella lobata and Siphonodella quadruplicata appear,
whilst in Tn2 C Siphonodella sexplicata makes its first appearance.

Tn2c is characterized by the presence of the genera Pseudopolygnathus, Siphono-
della and Elictognathus. The base of Tn2 C would appear to correlate with the upper
part of the Middle Hannibal Formation of North America, based on the first occur-
rence of the species Siphonodella cooperi and Siphonodella sexplicata.

At the base of Tn3 a in Belgium and France, the following species have their first

64 BRITISH AVONIAN CONODONT FAUNAS

occurrence : Gnathodus commutatus, Gnathodus delicatus, Gnathodus semiglaber and
Polygnathus communis. Siphonodella obsoleta and Siphonodella duplicata are also
present.

In the Avonian Gnathodus delicatus first appears in Z x . It is followed in the Lower
7,2 Subzone by Gnathodus simplicatus and in the upper part of Z2 by Gnathodus semi-
glaber. Thus the upper part of Z\ and the Z2 Subzone would appear to be broadly
equivalent in age to Tn3 a . There are, however, two peculiarities in the Franco-
Belgian Tn3 a conodont fauna : firstly, the late first occurrence of Polygnathus
communis, and secondly, the occurrence of Pseudopolygnathus triangulus inaequalis.

Tn3b is characterized in the Franco-Belgian Province by the presence of Gnathodus
delicatus, Polygnathus communis, Doliognathus excavatus, Scaliognathus anchoralis,
Hindeodella segaformis, Gnathodus bilineatus, Gnathodus homopunctatus and Gnathodus
girtyi.

In Germany two of these species, Scaliognathus anchoralis and Hindeodella sega-
formis, and also one of the genera, Doliognathus, are confined to the Scaliognathus
anchoralis Zone (Cu II (3/y). Gnathodus delicatus first appears at the base of the
anchoralis Zone. The youngest occurrence of Polygnathus communis is within the
anchoralis Zone. Gnathodus homopunctatus is present at the top of the zone, as too is
Gnathodus girtyi.

Gnathodus bilineatus in Germany does not appear until after the youngest strati-
graphic occurrence of Scaliognathus anchoralis (the anchor alis-bilineatus interval).
In the Franco-Belgian Province, on the other hand, the first appearance of the two
species is contemporaneous.

In the Franco-Belgian Province the youngest stratigraphic occurrence of the genus
Siphonodella coincides with the oldest stratigraphic occurrence of the genus Scalio-
gnathus at the base of Tn3 b . In Germany Siphonodella extends into Cu III a in the
Hartz Mountains of the Sauerland (Voges 1959). It extends into the same zone in
Spain (Dr W. Ziegler, personal communication) , but in North Africa (Dr G. Bischoff ,
personal communication) it is limited to Cu II. The Genus Elictognathus became
extinct a short distance beneath the anchoralis Zone, at the base of the upper
Siphonodella crenulata Zone (Middle Cu II a), whereas, in the Franco-Belgian
Province, the latter genus became extinct at the base of Tn3 a . Dr S. C. Matthews
is at present investigating the distribution of the anchoralis Zone fauna in Europe.

In North America the base of the Sedalia Formation is an unconformity and the
genera Elictognathus and Siphonodella have their youngest stratigraphic occurrence
at the top of the Upper Chouteau Formation. Scaliognathus anchoralis first appears
at the base of the Sedalia Formation. At the base of the Fern Glen Formation the
genera Doliognathus, Staurognathus and Bactorgnathus first appear. Gnathodus
delicatus, Gnathodus cf. girtyi, Gnathodus semiglaber , Gnathodus cuneiformis and
Gnathodus antetexanus also are present above the base of the Sedalia Formation.

In Germany there is a gap in the known conodont sequence beneath the anchoralis
Zone. It appears likely, however, that Tn3b of the Franco-Belgian succession is
equivalent in age to the German Cu II (3/y anchoralis Zone and the Cu II $ anchoralis-
bilineatus interval combined. It also correlates with the Fern Glen and Burlington

BRITISH AVONIAN CONODONT FAUNAS 65

Formations of North America. Pseudopolygnathus dentilineatus of Conil et al. in
Tn3b is synonymous with Pseudopolygnathus multistriatus of Mehl & Thomas in the
U.S.A.

This would also suggest that the Tournaisian-Visean boundary in the cephalopod
fades of Germany should not be drawn as at present at the top of Cu II a, but higher
in the succession at the top of Cu II.

There are, however, two complications. Firstly, the type fossil of the Cu II a
horizon, Pericyclus princeps, although never recorded from Germany, is recorded from
the Tn3 C horizon of Belgium. Secondly, Pseudopolygnathus triangulus inaequalis is
confined to Tn3 a in the Franco-Belgian Province and to the middle of the Cu I in
Germany. This might imply that the German Upper Cu I and Cu II a horizons are
equivalent in terms of the Franco-Belgian Tournaisian to the bedding plane boundary
of Tn3 a -Tn3b, but we have some reservations about the general applicability of the
subspecies of Ps. triangulus established by Voges.

In Britain none of the genera Scaliognathus, Staurognathus, Doliognathus, or
Bactrognathus have been found in the Avonian, although Matthews (1961) did record
Scaliognathus anchoralis, Hindeodella segaformis and Doliognathus lotus from the
Lower Carboniferous in East Cornwall. Thus these fossils, characteristic of the
anchoralis Zone in Germany were present in the British Lower Carboniferous seas.
One possible explanation of their non-appearance in the Avonian is that the
anchoralis Zone of Germany is represented in the Avonian by the Z2 Fish Bed, which
would thus represent a considerable non-sequence.

Alternatively Scaliognathus anchoralis and its typical zonal associates may be
limited in their distribution, either by fades or geography. This is supported by the
fact that in North America, from which it was first described, S. anchoralis is known
only from Branson & Mehl's type specimen, and further intensive sampling of the
type locality by Dr. C. W. Collinson has failed to produce even one additional
specimen (personal communication). It does not seem to be present in Australia,
although it is abundant in Germany, France, Belgium, Spain and North Africa.
Some of the typical associated genera display similar anomalies in distribution.
Doliognathus is abundant in some sections in Germany, but absent in others, even
though its zonal associates are present in both. It may be that this group of rather
bizarre genera are components of one or more natural conodont assemblages of
limited tolerance. If this alternative explanation is correct, the anchoralis Zone of
Germany may be represented not by a hiatus but by a succession with a different
fauna in the Avonian. The exact limits of correlation are difficult to determine,
but would lie within the Upper Z to Lower C Zones.

It seems possible, however, that the anchoralis horizon is equivalent to the lower
part of the Caninia Dolomite of the Avon Gorge, which has yielded no conodont
faunas.

VI. SYSTEMATIC PALAEONTOLOGY

The following section contains descriptions of the species recorded in the present
study. The ranges recorded in the descriptions refer to sample numbers that are
listed on p. 292.

66 BRITISH AVONIAN CONODONT FAUNAS

The following prefixes are used to describe the various collecting areas :

Avon Gorge : the section at the Avon Gorge, Bristol, and immediately adjacent

areas (see p. 18 and Figs. 59-69).
North Crop : the northern limb of the synclinal structure of the South Wales
Coalfield in Brecknockshire and Monmouthshire (see p. 22 and
Figs. 7, 70-73).
Scotland : the various sections from the Midland Valley of Scotland (see p. 29 and

Figs. 79-91).
Farlow : the Avonian section at Farlow, Shropshire (see p. 25 and Figs. 74-75).

In numbers of cases we have made use of open nomenclature in our specific and
generic assignments. We have followed this method where either the preservation
or numbers (or both) of specimens were so poor that we felt it unjustifiable to use a
formal name, even though we have sometimes recognized particular forms as
representing new species, and, in two cases, new genera.

Ranges for species are given only for the Avon Gorge and North Crop, except
where species are not present in these areas. Ranges for other areas are shown on
the appropriate range charts. In all cases, the ranges represent the maximum
distribution of the species, which may not always be present in every sample residue
between its first and last appearance. In most such cases, its absence is attributable
to particular samples proving barren or producing very low yields.

Catalogue numbers refer to specimens deposited in the British Museum (Natural
History).

Genus ANGULODUS Huddle 1934
1934 Angulodus Huddle : 76.

Type species. Hindeodella walrathi Hibbard 1927.

Angulodus walrathi (Hibbard)
Plate 29, fig. 8

1927 Hindeodella walrathi Hibbard : 205, text fig. 4a, b.

1934 Angulodus walrathi (Hibbard) Huddle : 77, PI. 4, fig. 15 ; PI. 10, fig. 5.

1934 Angulodus demissus Huddle : 77, PI. 10, fig. 15.

1940 Angulodus elongatus Stauffer (partim) : 419, PI. 58, figs. 1, 2 only.

non 1957 Angulodus walrathi (Hibbard) Bischoff : 17, PI. 5, figs. 44, 45.

non 1961 Angulodus walrathi (Hibbard) Higgins : 10, fig. 16.

Material. 21 specimens : figured, X 36.

Range. North Crop KL 3-ZLA 6, Avon Gorge Z 4-Z 37.

Description. An arched elongated unit, with a straight anterior bar which is
laterally compressed and deflected through 45 ° in a vertical plane. The anterior
bar bears a series of at least 6 fine, laterally compressed, confluent, posteriorly inclined
denticles, their apices being discrete. The apical denticle is about twice as high and
three times as wide as the other denticles, and is of the same general form. The

BRITISH AVONIAN CONODONT FAUNAS

posterior bar is about three times longer than the anterior bar and up to twice as
deep. The denticles are fine, laterally compressed, needle-like, fused for about half
their length, and posteriorly inclined at about 60 ° to the horizontal in the anterior
third. In the posterior portion, the inclination tends to increase, so that in the
recurved posterior terminus of the bar, the denticles lie parallel to the main posterior
bar. The denticles of the posterior bar tend to have a hindeodellid arrangement.
The posterior bar bears up to 23 denticles, about 18 of which he anterior to the
recurved posterior terminus. It has a straight aboral edge in the posterior two-
thirds. The basal cavity is small and confined to the area immediately anterior to
the apical denticle.

Posterior bar

Apical denticle

Posterior pa

of posterior

or bar

Anterior part
of posterior bar

Point of depression

Fig. 17. Angulodus sp. showing morphological terms used in the text.

Angulodus sp. nov. B
Plate 29, figs. 5a, b

8 specimens : figured, X 37.
and horizon. North Crop, River Clydach, Nr. Gilwern, upper part

Material.

Locality
of Lower Z Zone. Sample ZLA 14

Range. North Crop ZLA 8-ZLA 14, Avon Gorge Z 34-C 7.

Description. An Angulodus with robust bar, the short anterior portion being
depressed and deflected. Posterior bar up to five times as long as anterior, with 90 °
posterior depression. Stout discrete denticles.

The whole unit is robust. The bar bears rather rounded lateral faces, and lacks
any conspicuous lateral compression. The unit is depressed downward at both the

68 BRITISH AVONIAN CONODONT FAUNAS

posterior and the anterior extremities. The apical denticle is of the same size as the
denticles of the anterior bar. The anterior bar is short, depressed downward through
70 ° and deflected inward up to 90 °. It bears isolated sub-circular denticles, which
tend to increase in size anteriorly. The posterior bar is about four to five times as
long as the anterior bar. It is deflected through about 90 ° at its posterior termina-
tion, and bears irregular, isolated, sub-circular denticles, which increase in size
posteriorly to the point of depression, when they decrease in size towards the
posterior end. Those in the anterior portion of the posterior bar bear smaller
denticles (about one third the width of the larger ones) between them. In aboral
view the unit is excavated beneath the apical denticle and possesses an inverted basal
cavity over its whole length. Here and elsewhere " inverted " is used to describe a
basal cavity with wide flaring opening and more or less restricted internal form (see
Lindstrom 1964). This is visible as a basal flange in lateral view.

Angulodus sp. nov. C
Plate 29, figs. 3a~4c

Material. 18 specimens : figured, X 38, X 39.

Locality and horizon. North Crop, River Clydach, Nr. Gilwern, K and Lower
Z Zones. Sample ZLA 10.

Range. North Crop KL i-ZLA 14, Avon Gorge Z 34-Z 38.

Description. A simple, stout, short unit, with a few stout, isolated denticles ;
bars are deflected and depressed in at least two directions on the inner side.

The apical denticle is relatively small, sub-circular in cross-section, posteriorly
inclined and continuously curved at various angles towards the inner side. The
short, stout anterior bar is deflected through 90 ° and then depressed downward
through 90 °. It bears 3 to 4 massive, discrete, sub-circular denticles, which tend to
decrease in size distally. The posterior bar is massive and very short, the anterior
portion being about equal in length to the anterior bar and only slightly longer than
the posterior portion. It is stout, with broadly convex lateral faces, and is slightly
twisted. The posterior depression may be strong or gentle, but the distal end is
depressed through about 90° in both cases. It bears only 3 to 5 stout, sub-circular,
posteriorly inclined, isolated denticles, the largest being at the point of depression.

In aboral view the unit is expanded, the cavity being large and extremely shallow,
in some cases approaching an inverted basal cavity ; it is largely confined to the
anterior portion of the posterior bar (PI. 29, fig. 3c).

Remarks. This is a very unusual form, the only comparable species being
Centrognathodus spurius Branson & Mehl (1934 : 198). The present specimens differ
from this in the relative position of the basal cavity and the lack of an " outer spur ".
A form described as Angulodus demissus Huddle by Bischoff & Ziegler (1957 : 43) is
also similar. This latter form, which is not Angulodus demissus Huddle, could be
the same as our specimens. Angulodus sp. C differs from Angulodus sp. D in the
nature of the posterior termination.

BRITISH AVONIAN CONODONT FAUNAS 69

Angulodus sp. nov. D
Plate 29, figs. ia-2c

Material, io specimens : figured, X 40, X 41.

Locality and horizon. North Crop, River Clydach, Nr. Gilwern, upper part of
Lower Z Zone. Sample ZLA 11.

Range. North Crop ZLA 8-ZLA 14, Avon Gorge Z 34-Z 38.

Description. A simple bar unit similar to Angulodus sp. C but with a longer
anterior portion of the posterior bar and a less marked and distinctly denticulated
depression of the posterior termination.

The apical denticle is fairly small, sub-circular in cross-section, inclined posteriorly
and towards the inner side, so that it does not lie in the same plane as the other
denticles or the rest of the unit. The anterior bar is short, massive, deflected
through 90° ; horizontal or feebly arched upward and then depressed through 90 °.
It commonly bears 4 to 5 stout, irregular, isolated, sub-circular denticles, which tend
to be tallest in the anterior part. The anterior part of the posterior bar is one and a
half to twice as long as the anterior bar. The oral surface bears 3 to 4 discrete
pointed denticles, their diameter being about two thirds that of the apical denticle,
and their cross-sections sub-circular to biconvex. They are inclined at about 45 ° to
the posterior bar, and are separated by irregular smaller " hindeodellid " denticles.
They tend to decrease in size posteriorly towards the point of depression. The
posterior part of the posterior bar is depressed at an angle of 90 °. It is very short,
and its oral surface is limited to a single, large, fang-like denticle. This is strongly
laterally compressed, with flat to gently convex lateral faces, and anterior and
posterior edges. It lies almost parallel to the anterior part of the posterior bar.
The posterior termination of the unit is pointed to sharply spatulate. A minute
secondary denticle may be developed on the posterior edge of the most posterior
denticle. The basal cavity is confined to the area below the apical denticle. The
posterior bar commonly has a very fine aboral keel along its whole length.

In aboral view the sub-apical pit is large and extremely shallow, approaching the
form of an inverted basal cavity.

Remarks. A form similar to this species is described by Bischoff & Ziegler
(1957 : 43, PL 20, figs. 3, 6) as Angulodus gravis Huddle. The holotype of A. gravis
differs greatly from the specimens figured by Bischoff & Ziegler, but there is a marked
similarity between their forms and the present specimens.

Genus APATOGNATHUS Branson & Mehl 1934
1934 Apatognathus Branson & Mehl : 201.

Type species. Apatognathus varians Branson & Mehl 1934

Apatognathus bladus sp. nov.
Plate 20, figs. I5a-i6b

Derivation of name. From Latin blade.

70 BRITISH AVONIAN CONODONT FAUNAS

Diagnosis. Apatognathus in which denticles on anterior bar and apical denticle
have very conspicuous anterior and posterior keels developed on edges. They are
unusually wide and blade-like. Two largest denticles of anterior bar separated by
single denticle from apical denticle. Denticles of posterior bar adjacent to apical
denticle are minute. Whole unit sharply depressed at apex and strongly inwardly
twisted. Inner lateral faces of both bars bear conspicuous ridges near point of
contact with denticles and are flat to concave below these ridges.

Material. 8 specimens : Holotype X 45, Paratype X 46 (both figured).

Type locality and horizon. North Crop, Craig-y-dinas, Breconshire. Sample
CYD 7.

Range. North Crop CYD 7.

Description. Anterior bar of unknown length ; it is deep and thin, bearing
more than 4 strong, greatly laterally compressed denticles on its oral surface, the
largest two being separated from the apical denticle by a single small denticle.
The denticles of the anterior bar, as well as the apical denticle, are so strongly lat-
erally compressed that they have strong lateral keels developed on their anterior and
posterior edges. The combined width of these keels equals or exceeds the width of
the "core" of the denticles. The denticles are basally confluent but are discrete for
most of their lengths. They are inclined slightly posteriorly. Below the base of
these denticles the apical bar bears a conspicuous longitudinal ledge which is rounded
and parallels the oral surface of the bar. Below this ledge the aboral surface is
relatively wide and there is a slight ledge developed on its inner lateral face. It is not
conspicuously excavated. The apical denticle is strongly biconvex in cross-section
but the anterior and posterior edges are conspicuous features on both margins. It is
elongated, but is not conspicuously greater in width than the largest denticle on the
anterior bar. It is straight and tapers gradually. The posterior bar is only about
one-third the depth of the anterior, but it is thicker than it is deep. Its oral surface
bears a series of crowded, minute and more or less sharply pointed denticles. In
cross-section the posterior bar is more or less quadrate with a sharp longitudinal
ridge developed on the upper inner lateral face and a more or less smooth to flat outer
lateral face. Its basal surface is the widest part of the bar and is flat. In outer

Posterior bar

Apical denticle

Outer face

Twisted distally

Anterior bar
Inner face

Fig. 18. Apatognathus sp. showing morphological terms used in the text.

BRITISH AVONIAN CONODONT FAUNAS 71

lateral view the lateral walls of the bar and the denticle faces are flat, and the whole
unit is continuously recurved so that all denticles point inward. The slight lateral
flange on the outer aboral lateral face of the anterior bar and the wide posterior
aboral surface are conspicuous features.

Remarks. Although our specimens are fragmentary the distinctive size and
character of the denticles, as well as the form of the base, appear to set this species
apart from all those previously described.

Apatognathus chauliodus Varker
Plate 20, figs, ia, b, ; 2a, b
1967 Apatognathus ? chaulioda Varker : 129, 131, PI. 17, figs. 1-3, 5.

Material. 2 specimens : figured, X 44, X 550.

Range. Avon Gorge D 7.

Description. The bars diverge at an angle of 25°-35° and in inner lateral view
are inclined inwards to slightly face one another. The apical denticle is as wide as
the prominent bar cusps, widest at its base and sharply pointed. It is slightly
curved and inclined to the posterior. A prominent denticle is present on each of the
lateral bars. These bar cusps are equal in size to the apical denticle, bue characteristic feature of this species is its virtual bilateral

76 BRITISH AVONIAN CONODONT FAUNAS

symmetry. In the present specimen the two limbs diverge at an angle of about 45 °
in outer lateral view. The denticles stand more or less erect to the limbs towards
their distal extremities but they tend to radiate away from the apex ; they are
more or less sub-equal in size and closely similar in size on both anterior and posterior
bars. The apical denticle tends to be only slightly larger than the largest on the
bars, on which the largest denticles tend to be separated by a single denticle from
both the anterior and posterior edges of the apical denticle. The denticles are
confluent for about two-thirds of their length, with sharp anterior and posterior
edges and gently convex lateral faces. The whole unit is continuously recurved
inward and on both the anterior and posterior limbs there is a more or less con-
spicuous basal longitudinal ridge developed near the aboral margin. In inner lateral
view the whole unit is regularly and continuously concave. The bars of the present
specimens are of rather unequal length, the anterior bearing 9 denticles and the
posterior 8 ; it is probable that neither is complete, however.

Remarks. The present specimen bears a very close resemblance to Varker's
holotype in all features except the relative size of the apical denticle. In the present
specimen this is only about half the size of that in Varker's specimens. This does
not seem to us, at present, a valid reason for regarding the two forms as distinct
species. Varker notes that the processes of his specimens bear up to 20 or more
denticles.

We have used the name of this species as the zonal name for one of our zones.
The zone is characterized by the common occurrence of apatognathids, virtually all
of which are broken, however. Many of these resemble the present species, but they
are too fragmentary to include in the count of material.

Apatognathus sp. nov. A
Plate 31, fig. 22

Material. 2 specimens : figured, X 43.

Type locality and horizon. North Crop, River Clydach, Nr. Gilwern, Z Zone.
Sample ZLA 13.

Range. North Crop ZLA 13.

Description. A strongly arched Apatognathus with conspicuous apical denticle.
Slender recurved anterior bar has about 10 crowded denticles, and is curved in the
same plane as the apical denticle. Posterior bar stout, deep, deflected and depressed,
with 4-5 large, discrete denticles.

The unit is arched and bowed. The apical denticle is tall, laterally compressed,
with knife edges on the anterior and posterior margins, posteriorly recurved and
laterally inclined toward the inner side. The outer face is strongly, and the inner
face feebly, convex. The anterior bar lies in the same plane as the apical denticle
and is shallow and somewhat recurved. It bears about 10 laterally compressed,
posteriorly inclined, partially fused denticles. The deep posterior bar is deflected,
and depressed. It bears a series of 4 or 5 large, discrete, laterally compressed

BRITISH AVONIAN CONODONT FAUNAS 77

denticles, standing perpendicular to the bar, the largest developed at about midpoint.
The basal cavity is minute and is situated beneath the apical denticle.

Remarks. This form is very similar to Apatognathus} geminus (Hinde) of Rexroad
and Collinson (1963), our specimens differing only in that the posterior bar is more
strongly curved and twisted. This may not be specifically significant, and if the two
forms are identical, the range of the present form would be extended upward, into the
St. Louis Formation of the Upper Mississippi Valley. Rexroad and Collinson
(1963 : 7) point out that in North America there is a gap between the Upper
Devonian and Upper Visean record of Apatognathus. Our apatognathid fauna
appears to bridge that gap, and thus Apatognathus may not necessarily be a poly-
phyletic genus as Rexroad and Collinson suggest.

Apatognathus sp.

Plate 31, fig. 2

Material. 16 specimens : figured, X 318.

Range. Avon Gorge Z 36-D 32.

Description. Fragmentary apatognathids occur in various parts of the succes-
sion. The specimen illustrated represents one such form, though other broken
specimens show considerable variation. They are not sufficiently complete to make
it possible to refer them to individual species.

Genus CAVUSGNATHUS Harris & Hollingsworth 1933
1933 Cavusgnathus Harris & Hollingsworth : 200-201.
Type species. Cavusgnathus alta Harris and Hollingsworth 1933.

Description. Harris and Hollingsworth (1933) gave the following description
for the genus : 'This genus is erected to include those lanceolate plated conodonts
with no semblance of a median crest in the median oral channel. Outline of plate
lanceolate to claviform ; oral face of plate with complete, deep, median longitudinal
channel without crest and bordered by marginal rims ornamented with denticles,
nodes, corrugations, or combinations of the same ; posterior bar denticulate'.

Ellison (1941) gave the following revised description : 'Elongate platform-like
teeth with high sides, extending parapet-like above a median longitudinal trench,
one parapet continued into a free longitudinal blade and connected at the posterior
end to opposite parapet, whose length is limited by the length of the platform ;
aboral surface of platform smooth, deeply excavated as a longitudinally elongate,
laterally asymmetrical spathodid-like cup, pointed at each end, transversed by a
median longitudinal groove, which extends to the ends of the platform and along the
aboral edge of blade ; sides of platform somewhat constricted laterally above the
aboral margin, to produce a lip-like lateral margin of variable width ; oral surface of
platform more or less grooved transversely, oral edge of blade denticulate and
crenulate.

BRITISH AVONIAN CONODONT FAUNAS

For purposes of description, the blade is directed anteriorly. It is continued
posteriorly as the outer edge of platform, the blade parapet. The elevated inner edge
of the platform is the inner parapet.'

Remarks. Cavusgnathus bears a marked resemblance to the genus Mestognathus,
but the two are easily distinguished on the basis of their basal cavities, that of
Mestognathus being small and narrow and that of Cavusgnathus wide and flaring.

The anterior blade in the cavusgnathid group has hitherto been thought to be
confined to the outer side of the unit and to be lateral in position (Rexroad in
Lindstrom 1964 : 124). However, the present study has shown that the position
of the blade in Cavusgnathus varies through the section. In the K Zone it is both
medial and lateral in position, whereas in the Z to D Zones it is lateral in position.
Some forms in the Z Zone have been found with the blade on the inner side.

In North America it has hitherto been thought that Cavusgnathus developed from
Taphrognathus in the Late Valmeyeran (Rexroad and Collinson 1963). Cavus-
gnathus, however, makes its first appearance in the Avon Gorge in the basal beds of

Platform

Anterior —

— Posterior

Abora I edge

Inner lateral view

Basal
cavity

Outer side

Oral surface

Lot erol

ridges

Carino

Aboral view

Orol view

Fig. 19. Cavusgnathus sp. showing morphological terms used in the text.

BRITISH AVONIAN CONODONT FAUNAS 79

the Z Zone and an earlier origin must therefore be suggested. The writers believe
that Cavusgnathns may have had its origin in Spathognathodus plumulus sp. nov.

Cavusgnathus charactus Rexroad

Plate 13, figs. 6a~7d, I3a-c

1957 Cavusgnathus characta Rexroad : 15-16, PL 1, figs. 1, 2.

1961 Cavusgnathus characta Rexroad ; Rexroad & Collinson : PL 1.

1963 Cavusgnathus characta Rexroad ; Rexroad & Collinson : 8, PL i, fig. 29.

Material. 8 specimens : figured, X 59, X 61, X 62.
Range. North Crop CYD 7, Avon Gorge S 5-S 44.

Description. The diagnostic characters of this species are the general form of the
anterior blade, which consists of six to eight denticles with low rounded apices of
more or less uniform size, except for those in the anterior portion. The posterior end
of the blade is separated by a distinct undenticulated depression from the outer
lateral face of the posterior platform. The free anterior blade is not long in com-
parison with the length of the platform. In outer lateral view the platform decreases
in depth towards the posterior end. Its oral surface is bluntly crenulate and the
whole aboral surface of the unit is regularly concave. There is a conspicuous
thickening below the basal cavity, which is situated in the anterior portion of the
platform and the whole outer lateral edge of the blade is bevelled. In some speci-
mens there are only four or five denticles on the anterior blade, the most posterior
being the largest and most massive. They all stand more or less erect to the bar.
The oral margin of the platform is continuously convex in outer lateral view, the
outer parapet obscuring the inner, when seen in this direction. The blade tends to
decrease in depth posteriorly ; its anterior aboral corner is bluntly rounded. In
inner lateral view the basal cavity makes a conspicuous flaring feature on the aboral
surface, and the oral edge of the platform is strongly convex and irregularly crenulate.
The platform tends to show some narrowing anteriorly and its widest point is in the
posterior half. In the posterior half there is a median carina of variable length,
consisting of a number of rather conspicuous but fused, strongly laterally compressed
nodes. The carina extends beyond the posterior limit of the platform proper. The
platform edges are decorated with feeble transverse ridges and the whole median area
of the platform is excavated by a deep U-shaped trough, which runs parallel to the
anterior blade and does not decrease greatly in depth when traced anteriorly.

In aboral view the aboral cavity is widely flaring and asymmetrical, but the basal
pit itself is restricted to the anterior quarter of the platform. It is deep but not very
broad and is extended as a longitudinal slit to the posterior end of the unit, the
lateral edges of the lip gradually converging towards the posterior end. It is also
extended anteriorly for a short distance, though the inner lateral lip, when seen in
aboral view tends to be more widely flared than the outer, and also in some, though
not in all, specimens to extend further forward.

The total length of the blade is about one-third of the whole length of the unit.
The blade is free for about half its length.

BRITISH AVONIAN CONODONT FAUNAS

Remarks. In some specimens there is a slight asymmetry of the posterior
platform, the inner lateral posterior margin tending to be more strongly outflexed
than the outer. The platform is widest on its oral edge and, especially in its posterior
half, tapers rapidly towards its aboral margin.

Cavusgnathus convexus Rexroad
Plate 14, figs. 2a-d

1957 Cavusgnathus convexa Rexroad

1958 Cavusgnathus convexa Rexroad
1 961 Cavusgnathus convexa Rexroad

1964 Cavusgnathus convexa Rexroad

1965 Cavusgnathus convexa Rexroad

17, PI. 1, figs. 3-6.

Rexroad : 16, PI. 1, figs. 12-14.

Rexroad & Collinson : PI. 1.

Rexroad & Furnish : 670, PI. 111, fig. 1.

Rexroad & Nicoll : 17, PI. 1, figs. 14, 15.

Material. 5 specimens : figured, X 63.

Range. Avon Gorge S 20-S 41, North Crop 3D 13.

Description. The margins of the inner and outer parapet are straight. A deep
trough runs the length of the platform and occasionally a few nodes form a carina at
its posterior extremity. The parapets are ornamented by regularly spaced, trans-
verse ridges. In lateral view, the anterior blade is seen to consist of six laterally
compressed denticles, which are fused nearly to their apices. The anterior blade is
highest near, but not at, its posterior extremity and this gives the blade a convex
oral edge. The anterior blade, which is less than one third the total length of the
unit, is free for half its length. The oral edge is convex and the aboral edge is
straight to slightly arched. The posterior edge is rounded. The basal cavity is of
moderate depth and asymmetrical ; it is long, extending for two thirds the length of
the unit, and reaches the posterior extremity of the unit. The inner is more flared
than the outer. A keel runs from the anterior edge of the basal cavity to the
anterior extremity of the unit.

Cavusgnathus cristatus Branson & Mehl
Plate 14, figs. 3a-d

1940 Cavusgnathus cristata Branson & Mehl :
1947 Cavusgnathus cristata Branson & Mehl ;

(non PI. 20, figs. 7-10).
1953 Cavusgnathus cristata Branson & Mehl ;
1956 Cavusgnathus cristata Branson & Mehl ;

1956 Cavusgnathus cristata var. grandis Elias :

1957 Cavusgnathus cristata Branson & Mehl
naviculus.)

1958 Cavusgnathus cristata Branson & Mehl
1 96 1 Cavusgnathus cristata Branson & Mehl
1 96 1 Cavusgnathus cristata Branson & Mehl

177, PI. 5, figs. 26-31.
Cooper (partim) : 91,

PI. 20, figs. 4-6

Hass : 77, PI. 14, figs. 12
Elias : 115, PI. 11, figs. 1
115, PI. 11, figs. 12-14.
; Bischoff : 19, PI

-14.
-6.

2, figs. 7a, b.

[ = C.

Rexroad : 16, PI. 1,
Rexroad & Burton :
Rexroad & Collinson

figs. 15-17-
1151, PI. 138, fig.16.
: PI. 1.

Material. 8 specimens : figured, X 64.

Range. Avon Gorge D 26, North Crop 3D 14/15-3D 22.

BRITISH AVONIAN CONODONT FAUNAS 81

Description. The margin of the outer parapet of the platform is straight and
that of the inner parapet, convex. A deep trough is developed for the greater part
of the length of the platform, except for the posterior quarter of the platform, where
there is a short carina, which bears a few nodes. The platform is ornamented by a
number of transverse ridges of medium length, which extend into the trough. In
oral view the flaring of the basal cavity on its inner side is seen.

The anterior blade, which rises out of the outer parapet, slopes slightly towards the
anterior. The posterior three denticles of the anterior blade are highest. The
anterior edge of the anterior blade and the posterior edge of the platform are of equal
elevation. Half the length of the anterior blade is free. Aborally, the basal cavity is
asymmetrical and flared, there being a greater flare on the inner side than on the
outer.

Remarks. This species closely resembles Cavusgnathus convexus but differs from
the latter in that the basal cavity does not extend to the posterior extremity of the
unit. In addition C. convexus rarely bears a carina and has fewer and shorter ridges
in the surface ornamentation.

The present specimens show an even closer similarity to C. regularis Youngquist &
Miller (as interpreted by Rexroad & Nicoll 1965, PI. 1, figs. 16, 17) and this species
may be a junior synonym of C. cristatus Branson & Mehl.

Cavusgnathus naviculus (Hinde)
Plate 13, figs. I2a-d. Plate 14, figs, ia-d, 4a-6d

1900 Polygnathus navicula Hinde : 342, PL 9, fig. 5.

1928 Polygnathus navicula Hinde ; Holmes : 18, PL 7, fig. 14.

1947 Cavusgnathus cristata Branson & Mehl ; Cooper (partim) : 91, PL 20, figs. 7-10.

J 957 Cavusgnathus cristata Branson & Mehl ; Bischoff : 19, PL 2, figs. 7a, b.

i960 Cavusgnathus navicula (Hinde) Clarke : 23, PL 4, figs. 1-3.

i960 Cavusgnathus inflexa Clarke : 23, PL 3, figs. 17, 19.

1961 Cavusgnathus navicula (Hinde) Rexroad & Burton : 1151, PL 139, figs. 4-13.

1965 Cavusgnathus navicula (Hinde) Rexroad & Nicoll : 17, 18, PL 1, figs. 24, 25.

Material. 9 specimens : figured, X 65, X 66, X 67, X 68, X 69.

Range. North Crop 3D 22, Avon Gorge D 26.

Description. Unit slender and elongate in lateral view with short blade ;
long, tapering inner and outer lateral sides which are almost straight in oral view,
and are about two to three times as long as the blade. In oral view they are abruptly
tapered in their posterior quarter, and the lateral edges are finely serrated. The oral
surface is decorated by transverse lateral ridges, which converge, but do not meet,
towards the narrow, shallow central trough. This trough is deepest in the anterior
third ; on the inner lateral oral surface the ridges are obsolescent and are replaced
by rounded nodes. There are about 10 transverse ridges on the outer lateral face.
In the posterior third of the unit there is the development of a rather inconspicuous
carina, consisting of fine, elongate, node-like denticles joined by a thin median ridge.
The inner lateral aboral flange is conspicuous in oral view.

82 BRITISH AVONIAN CONODONT FAUNAS

In outer lateral view the unit is characterized by a rather straight median portion
of more or less even depth, both the oral surface and to a lesser extent the aboral
surface appearing straight-edged in lateral view. The basal apron of the outer
lateral margin is considerably less flared and deep than that on the opposite lateral
margin.

The anterior blade decreases rapidly in depth anteriorly and its aboral edge, though
straight, is depressed vertically. It bears about six oral denticles, of which only
the most posterior are conspicuous, the largest being the most posterior of the
series. The oral edge is bluntly crenulate and the whole outer lateral face is gently
convex or flat, the junction with the aboral edge below the main denticle being
concave. The posterior end of the unit is gently downflexed and the posterior aboral
terminus is bluntly spatulate in lateral view.

The posterior platform decreases in width towards the posterior end, the decrease
being especially prominent in its posterior quarter. The anterior edge of the
anterior blade falls sharply away in its anterior third, so that the anterior is vertical,
but is still minutely denticulate. In inner lateral view the most prominent feature
is the large, rounded, depressed apron above the aboral margin of the cavity. This
occupies about half the total length of the unit and is regularly and strongly convex.

In aboral view the cavity is also a conspicuous feature. The anterior half is wider
than the posterior, the anterior point of origin being below the apical denticle. The
point of maximum width is about one-third of the total length from the anterior end
and the cavity is terminated posteriorly about five-sixths of the total length of the
unit from the anterior end, so that the posterior aboral edge of the unit is blade-like.
The anterior aboral edge of the blade is also thin.

Cavusgnathus unicornis Youngquist & Miller
Plate 31, figs. 13a, b

1949 Cavusgnathus unicornis Youngquist & Miller : 619, PI. 101, figs. 18-23.

1947 Cavusgnathus cristata Cooper (partim) : 91, PI. 20, figs. 7-10 only.

1957 Cavusgnathus unicornis Youngquist & Miller ; Rexroad : 17, PI. 1, fig. 7.

1957 ' Cavusgnathus unicornis Youngquist & Miller ; Lys & Serre : 1042, PI. 2, figs. 3a, b.

1958 Cavusgnathus unicornis Youngquist & Miller ; Rexroad : 17, PI. 1, figs. 6-11.

1961 Cavusgnathus unicornis Youngquist & Miller ; Rexroad & Burton : 1152, PI. 138,

figs. 10-12.
1961 Cavusgnathus unicornis Youngquist & Miller ; Rexroad & Collinson : PI. 1.

1963 Cavusgnathus unicornis Youngquist & Miller ; Rexroad & Collinson : 9, PI. 1, figs.
26-27.

1964 Cavusgnathus unicornis Youngquist & Miller ; Rexroad & Furnish : 670, PI. 111, fig. 6.

1965 Cavusgnathus unicornis Youngquist & Miller ; Rexroad & Nicoll : 18, PI. 1, figs. 18-20.

Material. 131 specimens : figured, X 329.

Range. North Crop CYD 6-3D 14/15, Avon Gorge C 34-D 26.

Description. The most distinctive feature of this species is the conspicuously
large posterior denticle of the anterior blade.

In aboral view the cavity is a conspicuous feature of the unit. It tends to be

BRITISH AVONIAN CONODONT FAUNAS 83

asymmetrical in detail, the inner side being rather wider than the outer, and some-
times starting a little anteriorly to the outer. The widest part of the cavity occurs
in the anterior third. It is extended posteriorly as a narrow, elongate pointed cavity.
It is deepest in its anterior half.

In oral view the unit tapers regularly towards the posterior end, the narrowing
being especially conspicuous in the posterior fifth. It is widest near the position of
the largest denticle on the anterior blade and its sides are more or less straight,
though in a few specimens they may be gently convex. The inner and outer
parapets are ornamented by a number of transverse, parallel, straight ridges, which
tend to be node-like in younger forms. They are most strongly developed in the
anterior half and are relatively short, not reaching the broad, shallow, concave
trough, which extends along the median part of the platform. There is a tendency
for a slight central carina with two or three nodes to develop in the posterior one-
fifth or one-sixth of the unit. There is a very conspicuous median depression on the
inner side of the anterior blade and the inner anterior margin of the platform is
strongly deflected inwards. In lateral view the oral and aboral edges are gently
convex and the outer parapet is very slightly higher than the inner.

The anterior blade slopes sharply downward from the largest denticle on the
posterior end. Its anterior aboral margin is bluntly spatulate and it bears a series of
inconspicuous node-like serrations along its length. These tend to gradually
increase in size towards the posterior end, the posterior denticle being enormously
expanded. It is not very high, but it is greatly elongated anterio-posteriorly, so
that it resembles a shark fin, with a convex anterior edge and a straight or concave
posterior edge. It is bluntly pointed, with more or less flat lateral faces and blunt
anterior and posterior edges. The overall profile of the anterior blade may be gently
convex or straight. It is about one-third the total length of the unit, but only about
half of it is actually free of the platform. The anterior and posterior edges of the
unit are almost vertical.

Remarks. Rexroad (1958) remarked on the changes which occurred during
ontogeny. Similar ontogenetic changes have been noted in the present study. The
young specimens tend to be narrow, with parapets which are nearly straight. In
more mature specimens the platform broadens without a corresponding increase in
length and the flare of the inner lip of the basal cavity also increases. The number of
small denticles on the anterior blade, anterior to the prominent posterior denticle,
also increases. A feature of the juveniles, which Rexroad did not note, was their
tendency to develop a row of nodes on the parapet, rather than ridges.

Cavusgnathus unicornis resembles C. char actus and C. convexus in the convex out-
fine of the platform in lateral view. However C. unicornis is distinctive because of
the high posterior denticle of the anterior blade.

There is a tendency in some specimens for the outer lateral face to be offset near
the position of the largest denticle. The carina in the posterior portion of the
platform seems to occur only in the largest individuals.

Young individuals of this species from the present faunas agree with Rexroad's
description (1958 : 17). Older individuals in our D collections have been identified

84 BRITISH AVONIAN CONODONT FAUNAS

by Dr. Rexroad as C. naviculus. We suspect that C. unicornis may be synonymous
with C. naviculus.

Cavusgnathus ? sp. nov. A
Plate 9, figs, ioa-d

Material. 2 specimens : figured, X 70.
Locality and horizon. North Crop, ZLA 32.
Range. North Crop ZLA 32.

Description. A cavusgnathid with the anterior blade developed on the left side
when viewed from the posterior.

The unit is highly reminiscent of species referable to the genus Cavusgnathus but
the free blade is developed on the opposite side, that is, the left side, when viewed
from the posterior. The platform is long, sinuous and deep, being ornamented by
transverse ridges which become obsolescent towards the deep median trough. The
trough is sinuous, deep, deepening towards the anterior, with a suggestion of a carina
filling it near the posterior termination. The blade is broken, but can be seen to be
situated on the opposite side of the platform to known cavusgnathids ; it appears to
be high and formed of laterally compressed denticles.

In aboral view the basal cavity occupies the whole platform area, the lips being
flared, especially on the blade side, and on the posterior part of the non-bladed side.

Remarks. All known species of Cavusgnathus are asymmetrical units, the lateral
blade being found on one side only and no mirror images being known (Rexroad
in Lindstrom 1964 : 124). The above form is, in fact, a mirror image of a typical
individual of the genus Cavusgnathus.

Genus CLYDAGNATHUS gen. nov.

Derivation of name. From the River Clydach.

Diagnosis. A lanceolate, curved platform unit, with short anterior blade, an
elongate platform and medial trough. The blade is medial to lateral ; the platform
is ornamented and may bear a posteriorly restricted carina ; basal cavity asym-
metrical. The phylogenetic origin and stratigraphic range are described below
(P- 85).

Type species. Clydagnathus cavusformis gen. et. sp. nov.

Description. The blade is medial to lateral, short, and slopes anteriorly. The
platform is lanceolate, elongated, bowed and laterally curved. It bears variable
marginal ornament, ranging from nodes to transverse ridges. A medial trough is
present, except at the posterior end, where a short medial carina is sometimes present
which occasionally extends beyond the platform as a posterior blade. The asymmet-
rical cavity is expanded, but is medially situated beneath the platform. The unit
is not grooved.

Remarks. This genus is closely allied to Scaphignathus and Cavusgnathus.

BRITISH AVONIAN CONODONT FAUNAS

Many adult specimens of Scaphignathus (illustrated by Helms 1959) have a similar
appearance to juveniles of Clydagnathus. The present genus can be distinguished
by the lack of a carina on the oral surface of the platform (except at the posterior
extremity) and the distinct basal cavity. Clydagnathus can be distinguished from
Cavusgnathus by the general anterior closure of the oral trough, by the merging of the
marginal ornament with the blade, and by the lateral, rather than longitudinal,
expansion of the cavity. It is thought that Clydagnathus was derived from Spatho-
gnathodus plumulus plumulus by addition of nodes and lateral movement of the
blade. Scaphignathus probably arose from a polygnathid ancestor and Cavusg-
nathus was derived from Taphrognathus (Rexroad and Collinson 1963). Thus none
of the three broadly homoeomorphic genera Scaphignathus, Clydagnathus and Cavusg-
nathus is related genetically and their different positions in the stratigraphical
column justify the use of distinct generic nomenclature. The use of distinct generic
names is a reflection of their distinct phylogenetic origin as well as an aid to strati-
graphy, although the degree of morphological difference between them is less than
that between most other platform genera.

Clydagnathus cavusformis sp. nov.
Plate 1, figs. 9~i3d

Derivation of name. From the close resemblance to the genus Cavusgnathus.

Diagnosis. Clydagnathid with lateral anterior blade very short, plume-like and
sub-triangular in lateral profile, consisting of about four to six fused denticles with
free, bluntly chevron shaped tips, largest near the posterior end.

Posteri or

Anterior aboral tip

Inner latera I view

Outer side

Carina

Medial trough

Basal covity

Orol view

Aboral view

Fig. 20. Clydagnathus sp. showing morphological terms used in the text.

86 BRITISH AVONIAN CONODONT FAUNAS

Material. 20 specimens : Holotype X 75, Paratypes X 71, x 7 2 > X 73, X 74
(all figured).

Type locality and horizon. R. Clydach, Nr. Gilwern, K Zone. North Crop.
Sample KL 5.

Range. North Crop KL i-KL 12, Avon Gorge K 12-K 17.

Description. The blade is short, being only a quarter to a fifth the length of the
platform. It is lateral in position, sub-triangular in profile and bears 4 to 9 fused,
erect denticles with distinct apices. The largest denticle of the anterior blade is near
the posterior end. The anterior aboral tip is bluntly spatulate. The platform is
long and rather pointed, bearing lateral nodes separated by a medial trough, which
usually deepens anteriorly (e.g. PI. 1, fig. 11). In adult specimens the lateral ridges
may coalesce medially, to form a sharply sinuous longitudinal ridge in the posterior
portion, the medial trough then being confined to the anteriormost portion of the
platform (e.g. X 72, PI. 1, fig. 9). In other specimens the lateral ridges may be con-
tinuous across the platform dividing it into a series of isolated laterally elongated
troughs (e.g. X 73, PI. 1, fig. 10), with a more or less prominent longitudinal marginal
ridge on one side. The platform may be very slender, elongate and sinuous (e.g.
X 74, X 75, PI. 1, figs. 13, 11). The posterior part may bear a short restricted carina
of rounded, isolated nodes (e.g. X 75, PI. 1, fig. 11) which can be produced as a short
posterior blade. The inner oral rim of the platform is deflected through 80 °, at the
anterior end, so preventing the trough from opening anteriorly.

The cavity is large, asymmetrical with thickened lips and is conspicuously laterally
expanded.

Remarks. This species is closely related to C. gilwernensis, from which it differs
by having a lateral blade rather than a medial one. It can be distinguished from the
genus Cavusgnathus by the closed medial trough and the pseudopolygnathid type of
asymmetrical sub-circular basal cavity.

Clydagnathus darensis sp. nov.
Plate 2, fig. 6a-7d

Derivation of name. From the type locality at Daren Ddu.

Diagnosis. Clydagnathid with relatively low, short anterior blade, consisting of
4 or 5 more or less erect denticles, those at the anterior end being only slightly
smaller than those at the posterior.

Material. 23 specimens : Holotype X 77, Paratype X 76 (both figured).

Type locality and horizon. R. Clydach, Nr. Gilwern, Lower Z Zone. Sample
ZLA 27.

Range. North Crop ZL 3-ZLA 27, Avon Gorge K 17.

Description. The unit is asymmetrical, the blade always being on the right
when viewed from the posterior. The blade is low, consisting of 4 or 5 denticles all
of approximately equal height, the tallest denticle being either the posterior or the

BRITISH AVONIAN CONODONT FAUNAS 87

penultimate posterior. The platform is ornamented by two rows of irregular nodes.
The margins are separated by a shallow trough, which generally tends to close
towards the anterior, and occasionally possess a short carina at the posterior
extremity. The lateral denticles on the blade side of the platform tend to be rather
larger than those on the other side. In smaller specimens, the basally confluent
platform denticles have sharply pointed, discrete apices in lateral view, but they
become more blunt in larger specimens. The platform walls are deep, and the aboral
outline is straight over the anterior two-thirds, but the posterior one-third can be
deflected downwards, especially in smaller specimens.

In aboral view, the unit is excavated, the cavity being large, flaring and asym-
metrical, extending from nearly the posterior extremity of the platform to its
junction with the anterior blade.

Remarks. This species can be distinguished from all other clydagnathids by
the character of the blade.

Clydagnathus gilwernensis sp. nov.
Plate 2, fig. ia-d

Derivation of name. From the locality at Gilwern.

Diagnosis. Clydagnathid with short, high, medial, anterior blade, and short
posterior carina occasionally developed into a short posterior blade.

Material. 7 specimens : Holotype X 78 (figured).

Type locality and horizon. R. Clydach, Nr. Gilwern, K Zone. North Crop.
Sample KL 1.

Range. North Crop KL i-KL 6, Avon Gorge K 6.

Description. The anterior blade is short and situated medially. It commonly
bears three denticles, the posteriormost being the tallest and most massive. The
blade denticles, which have blunt or chevron tips, are laterally compressed, and are
fused at their bases. They decrease rapidly in size anteriorly. The anterio-aboral
portion of the blade is strongly protruding and bluntly spatulate in profile. The
platform is long, slender and posteriorly sharply pointed ; it has two lateral rows of
blunt, triangular lateral nodes, with a shallow medial trough which is filled at the
posteriormost extremity by a short carina of 2 to 4 nodes, which may extend beyond
the platform to give a short posterior blade. On some specimens the carina may be
absent.

In lateral view the posterior platform of young forms is " upstepped " relative to
the blade, but in mature specimens the unit is arched about the cavity.

In aboral view there is an asymmetrical medial cavity situated in the anterior
third of the platform. It has longitudinally thickened lips ; a faint groove some-
times runs a short distance either side of the cavity.

Remarks. In gross morphological terms C. gilwernensis is similar to Patrognathus
variabilis but the vastly different cavity, the distinctive blade and excavated medial
trough serve to distinguish it. It would appear that the two forms were the result

88 BRITISH AVONIAN CONODONT FAUNAS

of convergent evolution, since the ancestors of C. gilwernensis were of spathogna-
thodid stock. They may have been functionally similar.

Clydagnathus unicornis sp. nov.
Plate 2, figs. 2a~3d, 5a, b

Derivation of name. From the single large denticle on the blade.

Diagnosis. Clydagnathid with restricted anterior lateral blade, consisting
essentially of one large denticle ; median trough opens anteriorly ; basal cavity
elongated and symmetrical.

Material. 25 specimens : Holotype X 79, Paratypes X 80, X 81 (all figured).

Type locality and horizon. R. Clydach, Nr. Gilwern, Lower Z Zone. North
Crop. Sample Z 2A.

Range. North Crop ZL 4-ZLA 27, Avon Gorge Z 1.

Description. The unit is asymmetrical, the blade always occurring on the right
side viewed from the posterior, and consisting essentially of one large denticle, sub-
triangular in shape and posteriorly inclined. The tip of the denticle is sharply
pointed and the anterior edge convex, forming a continuous curve with the spatulate
antero-aboral margin of the blade. The anterior face of this denticle occasionally
bears 2 or 3 small denticles which are fused with it, so that only thin blunt apices
are visible.

The platform is uneven, consisting of two rows of low irregular marginal nodes,
separated by a very shallow, but rather wide, medial trough. A short carina may
sometimes be present in the posterior extremity. The platform walls are deep, and
on the basal faces are disrupted by the flaring of the lips of the basal cavity. In
lateral view, the marginal nodes are sharply pointed in smaller specimens, but blunt
or flat in larger specimens.

In aboral view the unit is excavated, the cavity being asymmetrical, expanded
more on the inner side than the outer. The cavity runs posteriorly, becoming
narrower and shallower towards the posterior termination. It is grooved along its
whole length.

Remarks. This species probably arose from Clydagnathus cavusformis by fusion
of the anteriormost blade denticles to give an essentially unidenticulate blade, and
by the elongation of the cavity, rather than the laterally expanded cavity of C.
cavusformis.

Clydagnathus sp. nov. A
Plate 2, figs. 4a-d

Material. 2 specimens : figured, X 82.
Range. North Crop KL 7-KL 13.

BRITISH AVONIAN CONODONT FAUNAS

Description. A clydagnathid with a high, equally tridenticulate anterior blade,
a short posterior blade, and a heavy asymmetrical basal cavity.

The unit is arched and triangular in cross-section. The blade is short and high,
consisting of three equal denticles fused into a blade but with free tips which are
slightly divergent. The platform is lanceolate, nearly four times as long as wide,
and is ornamented with two rows of denticles along the platform margins, separated
by a straight, shallow, smooth trough. The denticles tend to be transversely
elongate. The posterior part of the platform possesses a short carina, of about three
nodes, which is produced posteriorly to give a short posterior blade.

In lateral view the platform posterior to the basal cavity is deflected continuously
downwards through 30 °, and its depth decreases markedly towards the posterior.
The basal cavity is large, ovate, nearly symmetrical and is confined to the anterior
part of the platform ; it flares slightly in lateral view.

Remarks. This clydagnathid is similar to C. darensis, but the blade is much
higher, has fewer denticles and the deflected posterior platform is unique. The
cavity is also different in that all other clydagnathids have an obviously asymmetrical
cavity, whereas this form possesses a nearly symmetrical cavity.

Genus EUPRIONIODINA Ulrich & Bassler 1926

1925 Euprioniodina Bassler : 219. (nom. nud.)

1925 Synprioniodina Bassler : 219. (nom. nud.)

1926 Eupvio::'. ' .-; Ulrich & Bassler : 29.
1926 Synprioniodina Ulrich & Bassler : 42.

Type species. Eupvioniodina deflecta Ulrich and Bassler 1926.

Description. This genus is characterized by its general pick-shape, with a short,

denticulated, highly compressed anticusp.
numerous erect denticles.

The posterior limb is long and bears

Apical denticle

$. ^^.Dentlcles

Anterior bar

Posterior bar

Outer lateral face

Aborol margin

Fig. 21. Eupvioniodina sp. showing morphological terms used in the text.

go BRITISH AVONIAN CONODONT FAUNAS

Remarks. The genera Synprioniodina, Euprioniodina and Neoprioniodus have
essentially the same outline and differ in the presence, or absence, of denticles on the
anticusp. The genera Synprioniodina and Euprioniodina are here considered
synonyms and are characterized by a denticulated anticusp. Neoprioniodus is a
similar pick-shaped form to Euprioniodina, but has no denticulated anticusp.

As Scott and Collinson (1961) pointed out, there appears to be a number of forms
intermediate between Euprioniodina and Neoprioniodus. Sannemann (1955) »
Bischoff (1956) and Helms (1959) have assigned all such specimens to the genus
Prioniodina. However, the specimens they refer to Prioniodina do not closely
resemble the type species of Prioniodina, Prioniodina subcurvata. A detailed
revision of the pick-shaped forms is necessary, but as few specimens referable to the
genus Euprioniodina have been found in the present faunas, it is impossible to under-
take this study.

It is difficult to distinguish Euprioniodina from some species of Apatognathus.
We have divided the two genera by assigning to Apatognathus those species in which
there is conspicuous lateral flexing of one or both bars.

Euprioniodina caverna (Collinson & Druce)
Plate 22, figs. 11a, b

Synprioniodina caverna Collinson & Druce in press.

Material. 14 specimens : figured, X 83.

Range. North Crop 3D 14/15.

Description. The present specimens have a greatly elongated anterior bar,
which is more or less straight, and which bears a series of at least twelve laterally
compressed, confluent denticles on its anterior edge. These are small and of uniform
size, being considerably smaller than any of those on the posterior bar. The apical
denticle, which is aligned with the main line of the anterior bar, is relatively short ;
it is sharply pointed, with sharp anterior edges and a gently convex outer lateral face.
The junction of the anterior and posterior bars is marked by the development of an
apical lamella, which is depressed and has a flat surface in outer lateral view. The
posterior bar is straight to feebly convex in outer lateral view and is also flexed
inwardly. It bears a series of about 14 denticles on its oral edge, which show a broad
tendency to increase in size posteriorly, though this is not a regular feature. They
are basally confluent but apically discrete and are elongated and pointed, being at
least two to three times as long as those of the anterior bar. They are directed
forward parallel to the apicle denticle and are also curved gently inward.

In inner lateral view the surface of the posterior bar is gently convex, and that of
the anterior bar more or less flat. The denticles are distinctly curved inward and
there is a very sharp aboral flexure below the apical denticle with an angular to
strongly convex apical lamella.

The aboral surface is excavated by a narrow groove along the whole of its length,
this being a continuation of the wide flaring cavity below the apical lamella.

BRITISH AVONIAN CONODONT FAUNAS 91

Euprioniodina microdenta (Ellison)
Plate 22, figs. 16a, b

*933 Synprioniodina sp. Gunnell : 269, PI. 31, fig. 6.

1941 Synprioniodina microdenta Ellison : 108-111, 119, PI. 20, figs. 43-46.

1941 Synprioniodina microdenta Ellison ; Ellison & Graves : 3-4, PI. 1, fig. 10.

1944 Synprioniodina microdenta Ellison ; Branson : 327.

1952 Synprioniodina microdenta Ellison ; Rhodes : 893, PI. 126, fig. 4.

Material. 2 specimens : figured, X 84.

Range. North Crop 3D 4-3D 14/15.

Description. The present specimens are characterized by a very short anterior
bar and a greatly elongated posterior bar. In outer lateral view the posterior bar is
greatly elongated, tending to increase in depth posteriorly. Its outer lateral face is
flat to gently convex, and it is about equal in depth to the length of the free denticles.
Its oral surface bears about 14 long, slender denticles, more or less subcircular in
cross-section, though showing a slight tendency to lateral flattening. They are
discrete for most of their length and are sharply pointed. They are separated by
very much finer needle-like denticles, which are only a quarter to a third the width of
those of the major series. All denticles slope anteriorly, and are also more or less
curved inwards. They tend to increase in size towards the posterior third of the bar.
The outer lateral face of the main cusp is gently convex and it has conspicuously
sharp anterior and posterior edges. The anterior bar is very short, being only about
one-sixth the length of the posterior ; it tapers rapidly towards its distal end. It
bears 3 or 4 minute denticles, which lie parallel to the main cusp. In inner view the
whole unit is gently flexed, so that the inner lateral faces are very feebly concave.
The aboral margin of the posterior bar is more or less straight in lateral view, apart
from its rapid curvature below the apical denticle. The two bars diverge at an angle
of about 60 °. The apical denticle is about three times the width of the largest
denticles of the posterior bar.

Euprioniodina sp. nov. A
Plate 22, figs. 13a, b

Material, i specimen : Holotype X 86 (figured).

Locality and horizon. Hosie Limestone, Fife Coalfield. Sample HOSIE 2B.

Range. Scotland HOSIE 2B.

Description. A Euprioniodina with a massive, laterally compressed, incurved and
recurved apical denticle. The anterior bar is short and pointed with up to three
confluent denticles. The posterior bar is short with three minute denticles developed
on the posterior edge of the apical denticle.

The present specimen is very fragmentary, but it shows a massive apical denticle
which is laterally compressed with sharp anterior edges and gently convex lateral
faces. It is recurved sharply posteriorly in its lower portion. The short anterior
bar is pointed and bears a series of two or three confluent denticles on its oral edge

92 BRITISH AVONIAN CONODONT FAUNAS

which tend to decrease in size anteriorly. Three very small, confluent, laterally
compressed denticles are developed on the posterior edge of the apical denticle.
These are of minute size. The anterior aboral lateral face of the apical denticle is
very strongly expanded laterally, whereas that of the outer lateral face is flat to
feebly convex. The posterior bar is shallow and strongly laterally compressed, its
outer lateral face being flat and its inner very feebly convex. The apical denticle is
incurved as well as recurved.

Euprioniodina sp.
Plate 22, figs. 15a, b

Material. 16 specimens : figured, X 85.

Range. Avon Gorge K 4-K2 I.

Description. The apical denticle is relatively short and compressed, with a
denticulate anticusp equal in length to the apical denticle. The apical denticle is
strongly compressed laterally, with sharp anterior and posterior edges. The anticusp
is a continuation of the main denticle and both are slightly concave inward. The
anticusp bears up to 5 laterally compressed denticles, the anterior margins of which
are subparallel to the apical denticle. The posterior limb is long and thin, and is
sharply bowed immediately posterior to the apical denticle, with little additional
bowing behind this. The entire unit is sharply arched. The posterior limb is
straight and bears at least 14 confluent, sub-equal, sub-rounded to laterally com-
pressed denticles. The minute pit is located at the base of the cusp and has slightly
flared lateral lips. The pit is deep, with a sharp point extending into the base of the
apical denticle.

Genus GENICULATUS Hass 1953

x 953 Geniculatus Hass : 77.

Type species. Polygnathus ? claviger Roundy 1926.

Geniculatus sp.
Plate 31, fig. 24

Material. 2 specimens : figured X 327.

Range. Scotland DUN 59.

Description. Two broken specimens are present in one sample from Dunbar.
Both specimens are anterior bars which are greatly inflated and bear a series of
laterally compressed fused denticles with free chevron tips. In aboral view the bar
is broad and has a fine median groove.

Remarks. The inflated bar enables the present specimens, although broken, to
be referred to Geniculatus.

BRITISH AVONIAN CONODONT FAUNAS

Genus GNATHODUS Pander 1856
1856 Gnathodus Pander : 33.

Type species. Gnathodus mosquensis Pander 1856.

Gnathodus antetexanus Rexroad & Scott
Plate 18, figs. 6a-c, 8a, b, I3a-d

1947 Gnathodus texanus Roundy ; Mehl & Thomas : 10, PI. i, fig. 3.

x 957 Gnathodus texanus Roundy ; Bischoff (partim) : 25, PI. 3, fig. 22 only.

J 959 Gnathodus texanus Roundy ; Voges {partim) : 284, PI. 33, figs. 40, 42 only.

1962 Gnathodus n. sp. aff. Gnathodus texanus Roundy; Collinson, Scott & Rexroad : chart 3.

1964 Gnathodus antetexanus Rexroad & Scott : 28, PI. 2, figs. 7-10.

Material. 10 specimens : figured, X 412, X 413, X 414.

Range. North Crop ZLA 32-ZLA 33, Avon Gorge Z 33-C 9.

Description. Most of our specimens are broken, but the platforms are preserved.
They show the typical narrow outer platform, with a sparse covering of nodes, and
the broader inner platform with the large upstanding node, which are characteristic

Posterior Posterior

Outer side of

plotform

Node

Inner side of

platform

Carino

Blade

Basal cavity

Anterior
A. Oral view

Anterior
B. A bora I view

Denticles of blade

Nodes of platform
Carino

Platform

Blade

C Lot

eral view

Fig. 22. Gnathodus sp. showing morphological terms used in the text.

94 BRITISH AVONIAN CONODONT FAUNAS

features of the species. They are very similar to the specimens illustrated by
Rexroad and Scott.

Gnathodus avonensis sp. nov.
Plate 18, figs. o,a-d

Derivation of name. After the type section in the Avon Gorge.

Diagnosis. Gnathodus avonensis sp. nov. is closely similar to Gnathodus simplicatus
sp. nov. but bears a node on one side of upper surface of platform.

Material. 2 specimens : Holotype X 411 (figured).

Type locality and horizon. Avon Gorge Z2 Limestone. Sample Z 38.

Range. Avon Gorge Z 38.

Description. The platform is confined to the posterior third of the unit and is
unornamented except for the presence of a single node on one side of the platform.
It is biconvex in outline and narrow. In lateral view the blade is rather rectangular
in outline, the 10 or more denticles being of uniform size. The anterior edge is
straight, and forms a right angle with the aboral edge of the blade, which may be
slightly curved. The oral edge is straight in the anterior half of the unit and slightly
arched in the posterior half of the unit. The platform has a concave aboral margin
in lateral view, and is less deep than the blade. There is a flaring and elongate
basal cavity below the platform.

Remarks. Gnathodus avonensis sp. nov. developed from G. simplicatus sp. nov.
by the formation of a single node on the side of the platform. G. avonensis sp. nov.
is a homoeomorph of G. nodosus Bischoff.

Gnathodus bilineatus (Roundy)
Plate 18, figs. I4a-I7d

1900 Polygnathus [Gnathodus) Mosquensis Pander (sic) Hinde : 342, PI. 9, figs. 2-4.

1926 Polygnathus bilineatus Roundy : 13, PI. 3, figs, ioa-c.

1926 Polygnathus texanus Roundy : 14, PI. 3, figs. 13a, b.

1928 Gnathodus mosquensis (Pander) Holmes : 6, fig. 31.

1939 non Gnathodus bilineatus Cooper : 388, PI. 42, figs. 59-60.

1941 Gnathodus pustulosus Branson & Mehl : 172, PI. 5, figs. 32-39.

1953 Gnathodus bilineatus (Roundy) Hass : 78, PI. 14, figs. 25-29.

1956 Gnathodus bilineatus (Roundy) Elias : 118, PI. 3, figs. 23-29.

1956 Gnathodus pustulosus (Branson & Mehl) Elias : 115, PI. 3, figs. 1-8.

1957 Gnathodus bilineatus bilineatus (Roundy) Bischoff : 21, PI. 3, figs. 11, 15-20 ;

PI. 4. %• I-
1957 Gnathodus bilineatus bilineatus (Roundy) Ziegler in Flugel & Ziegler : 38, PI. 3, figs.
1, 2 only.

1957 Gnathodus modocensis Rexroad : 30, 31, PI. 1, figs. 15-17.

1958 Gnathodus modocensis Rexroad ; Rexroad : 17, 18, PI. 1, figs. 1, 2.

1959 Gnathodus bilineatus (Roundy) Voges : 282, PI. 33, figs. 28-30.

1959 Gnathodus (Harltonodus) bilineatus (Roundy) Elias : 145, PI. 1, figs. 3-12.

1959 Gnathodus (Harltonodus) bransoni Elias : 147, PI. 1, figs. 13-18.

1959 Gnathodus (Harltonodus) minutus Elias : 148, PI. 1, figs. 22-25.

1959 Gnathodus (Harltonodus) multilineatus Elias : 149, PI. 1, figs. 26-28.

BRITISH AVONIAN CONODONT FAUNAS 95

i960 Gnathodus smithi Clarke : 26, PI. 4, figs. 13-14 ; PI. 5, figs. 9 & 10.

1961 Gnathodus bilineatus (Roundy) Higgins : PI. 10, fig. 5.

1962 Gnathodus bilineatus (Roundy) Higgins : (partim), PI. 2, fig. 25 only.
1962 Gnathodus bilineatus bilineatus (Roundy) Meischner : 31, fig. 10.
1965 Gnathodus bilineatus (Roundy) Dunn : 1148, PI. 140, figs. 7-9.

Gnathodus bilineatus (Roundy) Collinson & Druce in press.

Material. 765 specimens, North Crop : figured X 416, X 417, X 93, X 94.

Range. North Crop 3D 10-3D 23.

Description. This is one of the most abundant species in the higher parts of the
section of the North Crop and, although it displays considerable variation, its main
features agree closely with those described by earlier authors, especially Hass (1953)
and Bischoff (1957). There is considerable variation in the ontogeny of this
species. The main variation concerns the increase in the relative size and angularity
of outline of the outer lateral platform, and its increasingly strongly developed
ornamentation. In young forms this tends to be inconspicuously nodose and
rather irregular, but in older forms it becomes either longitudinally linear or
broadly concentric in disposition, and the nodes become stronger, tending to form
elongate ridges. There is also considerable variation in the strength of the inner
lateral platform and of the transverse denticles developed upon it. In numbers of
specimens it is pinched inwards in the anterior half when seen in oral view. There is
also appreciable variation in the depth and relative width of the sulcus that separates
these denticles from the carina. In spite of its extent, the variation appears to be
continuous, and there is no obvious difference between specimens collected from
different parts of the range of the species.

Gnathodus commutatus (Branson & Mehl)
Plate 19, figs. ga-i2d

1941 Spathognatkodus commutatus Branson & Mehl : 98, PI. 19, figs. 1-4.

1941 Spathognatkodus commutatus Branson & Mehl ; Ellison & Graves : 3, 4. PI. 2,

fig. 6, (non PI. 2, fig. 4 = Gnathodus symmutatusl) .
1953 Gnathodus inornatus Hass : 80, PI. 14, figs. 9-1 1.

1956 Spathognatkodus commutatus Branson & Mehl ; Elias : 119, PI. 3, figs. 19-22.
1956 Spathognatkodus inornatus Hass ; Elias : 119, PI. 3, figs. 37-39.

1956 Spathognatkodus cf. inornatus Elias : 119, PI. 3, figs. 41, 42, (non PI. 3, figs. 62, 63 = G.
symmutatus?) .

1957 Gnathodus commutatus commutatus (Branson & Mehl) Bischoff : 22, PI. 4, figs. 2-6,

15-
J 957 Spathognatkodus cf. S. commutatus Branson & Mehl ; Rexroad : 38, PI. 3, figs. 23, 24.
? 1957 Gnathodus commutatus commutatus (Branson & Mehl) Ziegler in Flugel & Ziegler
39, PI. 3, fig. 21.

1958 Gnathodus inornatus Hass ; Stanley : 465, PI. 68, figs. 5, 6.

1958 Spathognatkodus cf. S. commutatus Branson & Mehl ; Rexroad : 26, PI. 6, fig. 8.

96 BRITISH AVONIAN CONODONT FAUNAS

non 1958 Gnathodus commutatus commutatus (Branson & Mehl) Lys & Serre : 891, PI. 9,
figs. 2a, b (-G. symmntatus) .

1959 Gnathodus commutatus commutatus (Branson & Mehl) Voges : 281.

1960 Spathognathodus commutatus Branson & Mehl ; Clarke : 19, PI. 3, figs. 4, 5.
i960 Gnathodus commutatus commutatus (Branson & Mehl) Serre & Lys : 39, fig. 3.

1961 Gnathodus commutatus (Branson & Mehl) Rexroad & Burton : 1153, PI. 139, figs.

i-3-

1961 Gnathodus commutatus var. commutatus (Branson & Mehl) Higgins : 212, PI. io,
figs. 6, text-fig. ia, (left figure only).

1962 Gnathodus commutatus commutatus (Branson & Mehl) Higgins : PI. 2, fig. 22.

1962 Gnathodus commutatus commutatus (Branson & Mehl) Meischncr : 31, text-fig. 10.

1963 Gnathodus commutatus commutatus (Branson & Mehl) Bouckaert & Higgins : 17,

ng- 3

1964 Gnathodus commutatus pellaensis Rexroad & Furnish : 671, PI. in, fig. 3.
Gnathodus commutatus (Branson & Mehl) Collinson & Druce in press.

Material. 425 specimens : figured, X 418, X 95, X 96, X 97.

Range. North Crop CYD 7-3D 22, Avon Gorge S 53.

Description. This species has recently been redefined by Collinson & Druce
(in press) and it is their revised description which is accepted here. Although the
species, which is represented by many specimens in the present collections, shows
appreciable variation, the distinctive characteristics are the regular sub-rectangular
outline of the blade when seen in lateral view, the regular height and thickness of the
confluent denticles which make up the blade, the rather square anterior profile of the
blade, and the small posteriorly restricted sub-oval to sub-circular unornamented
platform. This platform is always asymmetrical in detail, and shows considerable
variation in its basal outline and in the degree of flexure of its basal margin. This
variation is so obviously transitional, however, that it seems impossible to dis-
tinguish any discrete categories on the basis of it. The chief variation is in the
general form of the posterior platform, which varies from slenderly sub-elliptical to
sub-circular, in the degree of symmetry of the posterior platform, which is generally
marked by the inner margin being wider anteriorly than it is posteriorly, and in the
relation of the carina to the posterior margin of the platform. In some cases the
posterior margin of the platform tends to be relatively elongated, while in others it
tends to be bluntly rounded. The carina may, in some specimens, extend slightly
beyond the posterior margin when seen in oral view (PI. 19, fig. 9d) but in others it
terminates anteriorly to the margin. In a few cases the posterior portion of the
carina is strongly deflected laterally. In most individuals the central blade tends to
become thicker posteriorly, where it forms the carina of the posterior platform (e.g.
PI. 19, fig. iod). The surface of the posterior platform is smooth and the platform
itself occupies only the posterior quarter or third of the total length of the unit.
The broad variation within this species noted by Collinson and Druce is also shown
by the present specimens.

Remarks. In many specimens the blade is straight, but in others it is gently
curved in a horizontal plane ; in these cases the wider of the two platforms in the
anterior position is always that on the concave side of the blade.

BRITISH AVONIAN CONODONT FAUNAS 97

Gnathodus cuneiformis Mehl & Thomas
Plate 8, figs. 6a-c

1939 Gnathodus mosquensis Pander ; Cooper (partim) : 388, PI. 41, figs. 23-25 only ; PI. 42,

figs. 75, 76.
*939 Gnathodus stinus Cooper : 388, PL 14, figs. 40, 41.
1947 Gnathodus cuneiformis Mehl & Thomas : 10, PI. 1, fig. 2.
1962 Gnathodus cuneiformis Mehl & Thomas ; Collinson Scott & Rexroad : Chart 3, p. 10,

22, 23.

Material, i specimen : figured, X 98.

Range. Avon Gorge S 11.

Description. This species is characterized by a high, slightly asymmetrical,
arrow-shaped platform, bearing a single row of nodes on either side of the carina.
The flanks of the platform are smooth and steep.

Remarks. The shape of the platform and the single row of nodes on either side
of the carina distinguish this species from other gnathodids. In North America this
species is characteristic of the Sedalia, Fern Glen and Burlington Formations.

Gnathodus delicatus Branson & Mehl 1938
Plate 18, figs. I2a-d. Plate 30, figs. 6a-c

1938 Gnathodus delicatus Branson & Mehl : 145, PL 34, figs. 25-27.

1938 Gnathodus perplexus Branson & Mehl : 145, PL 45, fig. 24.

J 939 Gnathodus texanus (Roundy) Cooper : 388, PL 41, figs. 26, 27.

1951 Gnathodus delicatus Branson & Mehl ; Hass : 394, PL 46, figs. 3-7.

1957 Gnathodus commutatus punctatus Bischoff ; Fliigel & Ziegler : PL 111, figs. 16, 17, 24.

1959 Gnathodus delicatus Branson & Mehl ; Voges : 283, PL 33, figs. 31-33.

i960 Gnathodus delicatus Branson & Mehl ; Kronberg, Pilger, Scherp & Ziegler : PL 4,

figs. 7-12.

1962 Gnathodus delicatus Branson & Mehl ; Collinson, Scott & Rexroad : 10, Chart 3, 21, 22.

1962 Gnathodus delicatus Branson & Mehl ; Higgins : 13, PL 3, fig. 33 ; PL 2, figs. 23, 24.

1962 Gnathodus delicatus Branson & Mehl ! Zeigler : PL 4, fig. 4.

1963 Gnathodus delicatus Branson & Mehl ; Ziegler : 327, PL 2, figs. 5, 7, 8, 9, 13, 14.

1963 Gnathodus delicatus cuneiformis Ziegler : PL 2, fig. 12.

1964 Gnathodus delicatus Branson & Mehl ; Rexroad & Scott : 29-30, PL 2, figs. 4-6.

1964 Gnathodus delicatus Branson & Mehl ; Higgins, Wagner-Gentis & Wagner : 226, PL V,

fig. 24.
1964 Gnathodus cf. delicatus Branson & Mehl ; Higgins, Wagner-Gentis & Wagner : 226,

PL V, fig. 23.

Material, ii specimens : figured, X 87, X 426.

Range. North Crop ZLA 5-ZLA 6, Avon Gorge Z 28-Z 37.

Description. The asymmetrical platform of this species is ornamented by two
rows of nodes, one on the narrower inner side, and one on the wider outer side, both
running parallel to the carina. The inner platform bears a row of up to 9 denticles
parallel to the carina, and slopes steeply at its margin. The outer platform bears a
row of 5 denticles, parallel to the carina, on its inner side, and may also show traces of

98 BRITISH AVONIAN CONODONT FAUNAS

the development of a second row. There is a uniform sharp slope towards the
margin. The platform is arrow-shaped, being widest at the anterior. It becomes
pointed towards the posterior. The inner platform extends further anteriorly than
does the outer. The denticulate blade is equal in length to the platform. In lateral
view, the oral and aboral edges of the blade are straight ; the oral and aboral edges
of the platform are slightly curved. The anterior and posterior edges are straight.

Remarks. Specimens from the Z2 beds of the Avon Gorge have a row of nodes on
either side of the carina. In some examples, the anterior nodes of the inner side of
the platform are fused to form a parapet. These forms are considered to be transi-
tional with Gnathodus semiglaber, or possibly with Gnathodus antetexanus.

This species is common in conodont faunas of late Kinderhookian and early
Valmeyerian age in North America. Rexroad & Scott (1964) after studying
hundreds of specimens, came to the conclusion that the low, broad, asymmetrical
outline of the platform, and the linear arrangement of nodes seem to be consistent
characters, and similar specimens obtained in the present study have, therefore, been
placed in this species.

Gnathodus girtyi girtyi Hass
Plate 17, figs. ga-i2d

1953 Gnathodus girtyi Hass : 80, PI. 14, figs. 22-24.

1956 Gnathodus girtyi Hass ; Elias : 118, PI. 3, figs. 30, 31.

1957 Gnathodus girtyi Hass ; Bischoff (partim) : 24-25, PI. 4, figs. 16-17, 22-23 (non PI. 4,
fig. 21= Gnathodus girtyi simplex Dunn).

1957 Gnathodus girtyi Hass : Lys & Serre : 1043, PI. 1, figs. 7a-c.

1958 Gnathodus ? sp. Rexroad : 18, PL 1, figs. 3-5.

i960 Gnathodus clavatus Clarke : 28, PI. 4, figs. 4-6 (non PI. 4, figs. j—g = G. girtyi simplex

Dunn).
1961 Gnathodus girtyi Hass ; Higgins : 220, PI. 10, fig. 4.
1961 Gnathodus n. sp. Rexroad & Collinson : PI. 1.

1961 Gnathodus girtyi Hass ; Rexroad & Jarrell : 2015.

1962 Gnathodus girtyi Hass ; Collinson, Scott & Rexroad : Chart 4.

1962 Gnathodus girtyi Hass Form A Meischner : 31, text-fig. 10.

1963 Gnathodus girtyi Hass Form C Bouckaert & Higgins : 17, text-fig. 3.
Gnathodus girtyi girtyi Hass ; Collinson & Druce in press.

Material. 780 specimens : figured, X 103, X 104, X 105, X 106.

Range. North Crop CYD 5-3D 23, Avon Gorge D 26.

Description. The main features of this subspecies have been described in detail
by Collinson & Druce (in press) and the present specimens, although showing
some variation, agree in all major respects with their description. The most
distinctive features are the long slender form of the unit, with the anterior blade
commonly being strongly laterally compressed and relatively high in relation to its
length ; it occupies at least half the total length of the unit. It is straight to curved
in oral view. The unit as a whole is straight or curved in a horizontal plane, and the
curvature is chiefly concentrated in the posterior portion of the carina (e.g. PI. 17,

BRITISH AVONIAN CONODONT FAUNAS 99

figs, ii, 12). The blade is generally highest at its anterior end, although the two
most anterior denticles may be relatively small ; the posterior end of the unit tends
to be lower. The blade has a bluntly spatulate to rectangular anterior end and a
more or less straight or very feebly convex aboral edge. The denticles are fused to
about mid-height but their apices are discrete.

The carina consists of low, fused denticles, of about equal height to those at the
posterior portion of the anterior blade. The carina is depressed in the posterior half
of the platform, and the level of the denticles tends to be relatively higher than those
of the lateral ornament, which reaches about two thirds of the total depth of the
posterior platform from the top of the carina. The posterior platform itself is
characterized by a variably asymmetrical basal outline. In some specimens the
basal outline is almost biconvex, but in most the outer aboral margin is more con-
spicuously flared than the inner ; in a few individuals it is so strongly flared that it
gives to the basal outline a form reminiscent of such species as G. bilineatus or G.
semiglaber (e.g. PI. 17, fig. 12a). In spite of this, the platform ornament remains
distinctive ; the ornament on the inner lateral surface of the platform extends
further forward than that on the outer, and consists of a low series of fused nodes,
running sub-parallel to the carina but converging with it in the posterior platform,
and looping round the posterior end of the carina to give a bluntly rounded, pointed
outline (e.g. cf. PI. 17, figs. 11b, 12b). The outer platform ornament tends to be less
conspicuous than that of the inner ; the lateral ridges, which characterize the
denticles of the inner platform, are absent from the outer platform.

The basal cavity is flaring and asymmetrical, being deepest in the anterior third of
the platform and continuing for a variable distance below the posterior portion of
the anterior blade.

Remarks. In some individuals (e.g. PI 17, fig. 10b) the posterior carina tends to
continue somewhat beyond the level of the lateral denticles, which then tend to merge
with it anterior to the termination of the platform. In this they approach other
subspecies of the genus but are otherwise distinguishable from them.

Gnathodus girtyi collinsoni subsp. nov.
Plate 16, figs. 5a-8d

1962 Gnathodus girtyi Form C Meischner : 31, fig. 10.

1963 Gnathodus girtyi B Hass ; Bouckaert & Higgins : 17.

1965 Gnathodus roundyi Gunnell ; Murray & Chronic (partim) : 598, PI. 71, figs. 5, 6 only.

Derivation of name. After Dr. Charles W. Collinson.

Diagnosis. Subspecies of Gnathodus girtyi in which lateral denticulation of
platform is confined to inner lateral side. Very feeble nodes may sometimes be
developed on outer lateral platform.

Material. 13 specimens : Holotype X 99, Paratypes X 100, X 101, X 102 (all
figured) .

Type locality and horizon. North Crop. Sample 3D 14/15.

ioo BRITISH AVONIAN CONODONT FAUNAS

Range. North Crop 3D 8-3D 14/15.

Description. In broad morphology this subspecies resembles Gnathodus girtyi
girtyi. The form of the anterior blade, and its general denticulation, the general
outline and the size and depth of the posterior platform are generally similar. The
number of denticles in the main blade (including the carina) ranges from 21 to 25.

The distinctive feature of this subspecies is the denticulation of the posterior
platform. The inner-lateral oral surface of the platform has a conspicuously
developed, parapet-like series of denticles, those at the anterior end being higher than
those at the posterior. These denticles are individually rather small and incon-
spicuous, but the ridge which they form is itself made conspicuous by the general
height and thickness of the base. They number about 9, and are small rounded
discrete node-like structures. Those at the anterior end of the series are separated
from the carina by a shallow longitudinal groove. Towards the posterior end of the
series the denticles converge with the main carina, which they meet near the anterior
end of the fourth denticle from the posterior terminus of the unit. In lateral view
these denticles form a conspicuous shoulder-like feature of the platform. The
sloping anterior aboral margin terminates near the anterior end of the basal cavity.
On the outer lateral platform, very indistinct node-like denticles may sometimes be
developed but they are always a relatively inconspicuous feature, though in a very
few specimens they are barely discernible in both lateral and oral view (e.g. PI. 16,
figs. 7a-d).

Gnathodus girtyi simplex Dunn
Plate 16, figs. ia~4d

1957 Gnathodus girtyi Hass ; Bischoff : 24, 25, PI. 4, fig. 21 (non PI. 4, figs. 16, 17, 22, 23 = G.

girtyi girtyi Hass ; non PI. 4, figs. i8-2o = G. girtyi turritus Collinson & Druce.
1957 Gnathodus girtyi Hass ; Ziegler in Fliigel & Ziegler : 40-41, PI. 3, figs. 6, 9-13, 20.,
1957 Gnathodus bilineatus semiglaber Bischoff ; Ziegler in Fliigel & Ziegler : PI. 3, fig. 22

(non PI. 3, figs. 5, 8, 14, 2$ = Gnathodus semiglaber).
1959 Gnathodus texanus Roundy ; Voges : 284-285, PI. 33, figs. 40-43.
i960 Gnathodus clavatus Clarke (partim) : PI. 4, figs. 7-9 (non pi. 4, figs. 4-6= Gnathodus

girtyi girtyi Hass) .
1962 Gnathodus texanus Roundy ; Higgins : PI. 3, fig. 28.

1962 Gnathodus girtyi Form B Meischner : 31, text-fig. 10.

1963 Gnathodus girtyi Form A Hass ; Bouckaert & Higgins : 17, text-fig. 3.
1965 Gnathodus girtyi simplex Dunn : 1148, PI. 140, figs. 2, 3, 12.

Gnathodus girtyi simplex Dunn ; Collinson & Druce in press.

Diagnosis. Subspecies of G. girtyi in which lateral denticles on both inner and
outer lateral margins of platform are more feebly developed than in G. girtyi girtyi
and are also restricted to anterior and medial parts of platform.

Material. 260 specimens : figured, X 107, X 108, no, in.

Range. North Crop CYD 7A-3D 23, Avon Gorge D 26.

Description. In lateral and aboral views the main features of this subspecies are
closely similar to those of G. girtyi girtyi especially in the form of the anterior blade

BRITISH AVONIAN CONODONT FAUNAS ioi

and of the basal cavity. The most conspicuous difference is in the character of the
accessory lateral denticles on the posterior platform. The denticles on the inner
lateral platform are relatively more strongly developed than those on the outer.
They consist of up to 9 denticles, the highest and most massive being at the anterior
end, and are separated by a trough from the main median carina. Those towards the
posterior end of the series tend to be smaller and also to be developed nearer to the
carina. The denticles of the outer lateral platform are smaller and fewer in number
and extend further posteriorly than those on the inner lateral platform. In oral view
both series of lateral nodes converge posteriorly and fuse with the median carina, the
carina extending further posteriorly than either series of lateral denticles. In lateral
view the denticles of the inner series approach the height of those on the median
carina, but are still fractionally shorter. In outer lateral view the denticles at the
posterior end of the outer lateral series tend to be slightly larger and more con-
spicuous than those at the anterior end. The apron on the outer lateral platform,
when seen in oral view, is relatively much more laterally expanded than that of the
inner lateral platform. The denticles on the inner lateral platform tend to be
developed in a semi -transverse form, their outer edges being higher than their inner.
They show semi-radiate development around the central point of the inner lateral
platform, but this is not strongly marked in all individuals.

Remarks. This subspecies was recognized as a distinct group by Meischner
(1962) and Bouckaert & Higgins (1963).

Gnathodus girtyi soniae subsp. nov.
Plate 17, figs. 5a-8d

Derivation of name. After Miss Sonia J. Kostromin.

Diagnosis. Subspecies of Gnathodus girtyi resembling G. girtyi girtyi in having
ornamentation developed continuously around posterior platform and encircling
posterior termination of carina, but differing in development of 1 or 2 low rounded
inconspicuous nodes on outer-anterior-lateral surface of platform.

Material. 18 specimens : Holotype X 113, Paratypes X 115, X 112, X 114
(all figured).

Type locality and horizon. North Crop. Sample 3D 12.

Range. North Crop 3D 2-3D 14/15.

Description. A subspecies of Gnathodus girtyi with greatly expanded apron-like
posterior platform, the sides sloping sharply down. The median carina is strongly
developed and its posterior end is completely encircled by the lateral denticles of the
platform. The inner-lateral parapet is the highest single feature of the platform
ornament. It begins at a point anterior to the origin of the ornament, on the outer
lateral side, and has 3 or 4 massive laterally elongate denticles, the highest of which
tend to be those at the posterior end ; they are separated from the carina by a
narrow sulcus, which opens anteriorly into a siphonodellid-like spout. The denticles
decrease posteriorly in size, and are arranged as a linear series of low node-like forms.

io2 BRITISH AVONIAN CONODONT FAUNAS

On the outer-lateral margin of the platform one or two low rounded denticles are
developed. These tend to be developed about midway along the length of the
platform, and are visible but not conspicuous in lateral view.

The aboral cavity is large and flared, and the quadrate outline of the outer lateral
margin of some specimens is strongly reminiscent of G. bilineatus.

Gnathodus girtyi turritus Collinson & Druce
Plate 31, fig. 23

1957 Gnathodus girtyi Hass ; Bischoff : 24, 25, PI. 4, figs. 18-20 [non figs. 16, 17, 22, 23 =
Gnathodus girtyi girtyi Hass ; non pi. 4, fig. 21 = G. girtyi simplex Dunn).
Gnathodus girtyi turritus Collinson & Druce in press.

Material. 5 specimens : figured, X 116.

Range. North Crop 3D 19-3D 23.

Description A subspecies of G. girtyi with a low posteriorly reduced carina.
The lateral denticle ridges are generally continuous around the posterior edge of
the platform. The sides of the posterior platform are nearly vertical.

Remarks. The subspecies is extremely rare in our collections. Transitional
specimens of G. girtyi girtyi are present in faunas from Yorkshire and the North Crop.
It is difficult to refer these transitional specimens to one or other subspecies with any
certainty.

Gnathodus girtyi subsp. nov. A
Plate 17, figs. ia-3d

Material. 3 specimens : figured, X 117, X 118, X 119.
Range. North Crop CYD 7.

Description. A subspecies of G. girtyi characterized by the development of 1 or
2 vertical lateral pillars near the anterior inner end of the platform. The pillars
extend from the oral surface almost to the aboral margin.

The three specimens upon which this new subspecies is based show the general
features which are characteristic of G. girtyi girtyi. They differ from that subspecies,
however, in being left forms in which the longer inner lateral denticulated margin of
the platform is produced downwards by an unornamented, vertical column. In one
specimen (PI. 17, figs. 3a-d) this column reaches the aboral margin which is deflected
by it. In this particular specimen the vertical pillar occurs about one quarter of the
platform length behind the anterior end of the inner lateral denticle ridge. In the
specimen illustrated in PI. 17, fig. I, the vertical pillar occupies the same relative
position but is much less conspicuous, and the lateral margin only is conspicuously
offset by it. In this specimen the oral margin of the denticulation is not disturbed in
any way by a development of the lateral pillar. In the specimen shown in PI. 17,
fig. 2, two sharply angular vertical ridges are developed in the same relative position,
but neither of these extends into the aboral margin ; between them there is a

BRITISH AVONIAN CONODONT FAUNAS 103

regularly " U " shaped concave depression in the lateral face ; their upper termina-
tions are bluntly pointed, and in this case they are joined to the main ridge of plat-
form denticles by inconspicuous lateral ridges, although the denticle line is not
broken by them. The ridge is not denticulated or ornamented in any obvious way
in any of the three specimens.

Remarks. It is possible that these three forms are pathological variants of G.
girtyi girtyi but their restriction to a single sample and the fact that all three are left
lateral forms makes this seem unlikely.

Gnathodus homopunctatus Ziegler
Plate 19, figs. 5a-8d

1957 Gnathodus commutatus punctatus Bischoff : 24, PL 4, figs. 7-11, 14.
-non 1957 Gnathodus commutatus punctatus Bischoff ; Ziegler in Fliigel & Ziegler : 40 (PI. 3,

fig. 16 = juvenile of Gnathodus bilineatus punctatus (Cooper) 1939 ; PL 3, figs. 17,

24 = Gnathodus sp.).
J959 Gnathodus commutatus homopunctatus [Ziegler] Voges : 281.
i960 Gnathodus commutatus homopunctatus Ziegler : 39, 5, PL 4, fig. 3 (nom. nov. for

Gnathodus commutatus punctatus Bischoff 1957 non Cooper 1939).

1961 Gnathodus commutatus homopunctatus Ziegler ; Higgins : PL 10, fig. 9, text-fig. ic.

1962 Gnathodus commutatus homopunctatus Ziegler ; Higgins : PL 2, fig. 21.
Gnathodus homopunctatus Ziegler ; Collinson & Druce in press.

Material. 146 specimens : figured, X 120-X 123.

Range. North Crop CYD 7-3D 14/15.

Description. There is some similarity and degree of transition between this
species and G. symmutatus, but the present species differs in having a relatively
shorter and more symmetrical posterior platform, with the development of more
conspicuous denticulation. There is some variation in this denticulation ; in
immature specimens (e.g. PI. 19, fig. 5c) it is barely developed, and is present only as
rather dark, slightly elevated lateral ridges. In other specimens it tends to be
arranged at an acute angle to the anterior part of the blade, and consists only of
short barb-like lines of denticles. In most specimens, however, it forms more or less
symmetrical lines of low blunt denticles, developed parallel to the outer margin of the
platform, about midway between its lateral margin and the position of the carina.
In most individuals the development on the two sides of the carina is equal, but in
others it is asymmetrical.

Gnathodus mononodosus sp. nov.

Plate 19, figs. I3a-i5d

1 96 1 Gnathodus commutatus var. nodosus Bischoff ; Higgins : PL 10, fig. 7 only, text-fig. ib.

Derivation of name. From single node on the inner side of cup.

Diagnosis. Straight to slightly curved blade with subcircular to sub-quad-
rangular cup, bearing strong, generally elongate node on inner side.

104 BRITISH AVONIAN CONODONT FAUNAS

Material. 230 specimens : Holotype X 124, Paratypes X 125, X 126 (all
figured).

Type locality and horizon. North Crop. Sample 3D 14/15.

Range. North Crop CYD 7-3D 19.

Description. The blade is generally slightly curved. In lateral view both the
oral and aboral outlines are nearly straight, although the anterior is slightly higher in
some specimens. The denticles tend to be larger and more distinct at the anterior
end and become increasingly small and fused toward the posterior. Most are fused
to their tips. Both ends of the blade are nearly vertical in most specimens. The
posterior end of the cup may project beyond the blade.

In oral view the cup is characteristically sub-quadrangular and slightly asym-
metrical. The inner half bears a single node which is characteristically large and
elongate but in some specimens round. The blade is typically more than twice the
length of the cup.

Remarks. This species is very close to G. nodosus. That it is not merely a
random variant of nodosus, in which one or the other node is undeveloped, is shown
by the fact that the single node occurs only on the inner side of the cup.

The present specimens tend to show all the main forms of variation exhibited in the
platform by G. commutatus. They also show the rectangular profile of the blade of
that species when seen in lateral view, and also the relative variation in the curvature
and termination of the carina on the posterior end of the platform. In a very few
specimens the outline of the platform is more reminiscent of G. symmutatus, but it
differs from that species in having the square lateral profile of the blade, the oral
surface being of more or less uniform height, and not showing the pronounced
decrease in size of the posterior denticles over most of the length of the platform
(see p. 108).

In a few specimens the inner platform is more elongate than in typical members of
the species, the anterior margin being elongated at right angles to the line of the
blade. These individuals are further distinguished by the presence of two denticles
on the inner platform developed in a line lying at about 45 ° to the blade and pointing
anteriorly, and both being rather laterally compressed and basally confluent but
with more or less distinct apical tips. These specimens are so close in every other
respect to those with a single denticle, that there seems no good reason for separating
them.

In some specimens the denticle is not fully developed, but is represented by a slight
swelling occupying the same relative positions on the inner lateral platform, and
directed at about 45 ° to the anterior portion of the blade. There are transitions
between this partial development of the denticle and full development of the denticle
itself.

Gnathodus nodosus Bischoff
Plate 19, figs. i6a-20c

x 957 Gathodus commutatus nodosus Bischoff (partim) : 23-24, PI. 4, figs. 12, 13.

1957 Gnathodus commutatus nodosus Bischoff ; Ziegler in Fliigel & Ziegler : 40, PI. Ill, fig. 4.

BRITISH AVONIAN CONODONT FAUNAS 105

1958 Gnathodus commutatus nodosus Bischoff ; Lys & Serre : 891, PI. 9, figs. 3a, b, 4a, b.

1961 Gnathodus commutatus var. nodosus Bischoff ; Higgins (partim) : 213, PI. 10, figs. 8
(non fig. 7) ; text-fig. ib (non figs, in lower left or in uppermost left).

1962 Gnathodus nodosus Bischoff ; Higgins : PI. 2, fig. 19.

1962 Gnathodus comm. nodosus Bischoff ; Meischner : 31, text-fig. 10.

1963 Gnathodus commutatus nodosus Bischoff ; Bouckaert & Higgins : 17, fig. 3.
Gnathodus nodosus Bischoff ; Collinson & Druce in press.

Material. 220 specimens : figured, X 509, X 510, X 127, X 128, X 129.
Range. North Crop 3D 10-3D 22.

Description. This species shows some characteristics with both G. mononodosus
and G. commutatus. These include the posteriorly restricted laterally expanded
sub-circular to asymmetrical platform, and the rectangular lateral profile of the
uniform blade. The distinctive feature of the present species is the development of
denticles on both sides of the posterior platform. These are generally unevenly
developed, the one on the inner lateral side (represented by the concave lateral
flexure of the blade) generally being the more strongly developed of the two. Where
the denticles are more strongly developed, they tend to make angles of 45 ° with the
anterior part of the blade and to be laterally elongate. In some specimens the outer
lateral denticle is very feebly developed in comparison with the inner, but wherever
there is a suggestion of such bilateral denticle development, specimens are included
in the present species. Like the other species referred to above, this species shows
considerable but continuous variation in the symmetry and degree of lateral expan-
sion of the posterior platform, the form of the denticles, and the relationship of the
posterior portion of the carina to the posterior end of the platform ; there is also
variation in the degree of lateral deflection of the blade, and the outer lateral denticle
may also be developed posterior to the position of the inner lateral denticle.

The blade is similar in general form to that of G. commutatus and G. mononodosus,
having about 15 to 20 regular denticles, fused almost to their tips, and developing
straight oral and aboral margins. There is a tendency in some specimens for the two
anterior denticles to be relatively larger than the rest (e.g. PI. 19, fig. 18a). The
basal cavity is wide and flaring.

Gnathodus punctatus (Cooper)
Plate 18, figs, ia-c, ioa-nd

!939 Dryphenotus punctatus Cooper : 386, PI. 41, figs. 42, 43, PI. 42, figs. 10, 11.

1939 Dryphenotus litus Cooper : 386, PI. 42, figs. 34, 35.

J 939 Dryphenotus macrolobus Cooper : 386, PI. 41, figs. 48, 49 ; PL 42, figs. 45, 46.

1939 Dryphenotus oxys Cooper : 386, PL 42, figs. 12, 13.

1944 Gnathodus {Dryphenotus) macrolobus Cooper; Branson & Mehl : 245, PI. 94, fig. 69.

1951 Gnathodus punctatus (Cooper) Hass : 2539, PL 1, fig. 2.

non 1957 Gnathodus commutatus punctatus Bischoff ; 24, PL 4, figs. 7-1 1, 14.

1957 Gnathodus bilineatus semiglaber Ziegler in Fliigel & Ziegler : PL in, fig. 23 only.

non 1957 Gnathodus commutatus punctatus Bischoff ; Ziegler in Fliigel & Ziegler : 40, PL 111,
figs. 16, 17, 24.

J 959 Gnathodus punctatus (Cooper) Hass : 395, PI. 47, figs. 11-18.

io6 BRITISH AVONIAN CONODONT FAUNAS

1959 Gnathodus punctatus (Cooper) Voges : 283-284, PI. 33, figs. 34-37.

i960 Gnathodus punctatus (Cooper) Kronberg, Pilger, Scherp & Ziegler : PI. 4, figs. 15-18.

1963 Gnathodus punctatus (Cooper) Ziegler : PI. 2, fig. 4.

Material. 13 specimens : figured, X 131, X132, X 133.

Range. Avon Gorge Samples Z 33-38.

Description. This species is characterized by the adult specimens having the
nodes of the inner and outer sides of the platform fused with those of the carina in the
posterior two thirds of the platform. The pattern of nodes on the platform is also
characteristic, there being four rows, radiating from the junction of the platform and
blade. The platform is asymmetrical, being widest at the anterior end and pointed
at the posterior ; the outer side is wider than the inner. In juvenile examples the
carina is high, but in adult specimens the carina is fused with a row of nodes on the
inner and outer sides of the platform. A double row of nodes is present on the outer
side in fairly juvenile examples, but frequently there is only one row of nodes
developed on the inner side in juveniles. The blade is slightly longer than the
platform.

Remarks. Hass (1959) has illustrated growth stages of this species. The
specimens obtained in the present study most closely resemble those figured by Hass
in PI. 47, figs. 12, 13. Typically, the smaller inner side of the platform bears one
node, whereas the wider outer side of the platform has a few scattered nodes. The
outer side of the platform extends to the posterior tip of the unit. The inner side of
the platform does not extend to the posterior tip of the unit, but extends further to
the anterior than does the outer side of the platform.

In North America Gnathodus punctatus is abundant in the middle faunal zone of
the Chappel Limestone, and also occurs in the Siphonodella cooperi and Bactro-
gnathus communis zone. In the Avon Gorge it is characteristic of the Z 2 beds.

Gnathodus semiglaber Bischoff
Plate 30, fig. 1

1947 Gnathodus perplexus (Branson & Mehl) Mehl & Thomas : 10, PI. 1, fig. 4.

1957 Gnathodus bilineatus semiglaber Bischoff : 22, PI. 3, figs, ia, b, 2-10, 12-14.

1957 Gnathodus bilineatus semiglaber Bischoff ; Ziegler in Fliigel & Zeigler : p. 38, 1. pi 11,

figs. 5, 8, 14, 19 only (non pi. in, fig. 23 = Gnathodus punctatus, PI. IV, fig. 11, non PI. 3,

fig. 22 = Gnathodus girtyi simplex Dunn).
1959 Gnathodus semiglaber Bischoff ; Voges : 285, PI. 33, figs. 38, 39.
i960 Gnathodus semiglaber (Bischoff) Ziegler in Kronberg, Pilger, Scherp & Ziegler : PI. 4,

figs. 3-6.
1962 Gnathodus semiglaber (Bischoff) Collinson, Rexroad & Scott : 10, 22, Chart 3.
1962 Gnathodus semiglaber (Bischoff) Higgins : 13, PI. 3, fig. 26.
1962 Gnathodus semiglaber (Bischoff) Miiller : 1388, fig. 1.
1962 Gnathodus semiglaber (Bischoff) Meischner : 31, text-fig. 10.
1964 Gnathodus semiglaber (Bischoff) Rexroad & Scott: 30, PI. 2, figs. 1, 2.

Material. 3 specimens : figured, X 421.
Range. Avon Gorge Z 28-Z 30.

BRITISH AVONIAN CONODONT FAUNAS 107

Description. This species, which is well known and widely distributed in both
Europe and North America, is characterized by a low, small parapet on the inner side
of the platform, and a few scattered nodes developed on the middle part of the low
outer side of the platform. The carina tends to be laterally expanded in the posterior
part of the platform. Our specimens of this species agree closely with those described
by other authors.

Gnathodus simplicatus sp. nov.
Plate 8, figs. 5a-c. Plate 18, figs. 2a-5b

1957 Spathognathodus subrectus Holmes ; Fliigel & Ziegler : 53, PI. 11, fig. 12.
i960 Spathognathodus strigosus Branson & Mehl ; Dvorak & Freyer : PI. 1, fig. 17.

Derivation of name. From the simple form.

Diagnosis. A species showing Spathognathodus-Gnathodus transition, with
characteristic anterior blade, its highest point being at or near the anterior end, and
with oral surface sloping regularly towards the posterior end of unit. Platform very
feebly developed.

Material. 105 specimens : Holotype X 89, Paratypes X 88, 90, 91, 415 (all
figured).

Type locality and horizon. North Crop. Sample ZLA 33.

Range. North Crop ZLA 15-ZLA 33, Avon Gorge Z 33-Z 38.

Description. The unit is slightly bowed and slightly arched, highest in the
anterior quarter, and sloping posteriorly. The anteriormost one to three denticles
may be slightly shorter than the penultimate denticles, but otherwise the oral
outline is straight to slightly convex. The denticles, which number 13 to 15, are
small and laterally compressed with free chevron tips. The basal cavity is situated
in the posterior half and runs to the posterior termination ; the lips flare over the
whole length and the cavity widens to the mid-point where it becomes constricted
and then runs as a narrowing groove towards the anterior. The basal margin is
lipped and slightly stepped in lateral view.

Remarks. Middle and Upper Devonian forms similar to those described above
have been named as Spathognathodus bidentatus by Bischoff and Ziegler (1957) and
Freyer (1961). Bischoff and Ziegler's specimens have a greater number of denticles
(about 17 total) than ours, and the cavity is different, not quite reaching the posterior
end, and being greatly flared anteriorly. Freyer's specimens have only about 10
denticles and are much lower towards the posterior.

The present species is transitional between Spathognathodus and Gnathodus, but is
included in Gnathodus because the basal cavity is developed posteriorly, is longi-
tudinally extended, and the lips show a tendency to lateral flare.

There is some similarity between the forms described here andS. cristulus, which is
considered by American workers to be the basic stock for all spathognathodid
lineages. It is possible that the two species are the root stocks for successive
gnathodid developments, the genus Gnathodus being polyphyletic

io8 BRITISH AVONIAN CONODONT FAUNAS

In a few specimens the highest denticles are developed above the anterior end of
the basal cavity (e.g. PI. i8, fig. 2c ; X 89). In all other respects, however, these
specimens resemble the holotype.

Gnathodus symmutatus sp. nov.
Plate 19, figs. ia-4c

? 1941 Spathognathodus commutatus Branson & Mehl ; Ellison & Graves : PI. 2, fig. 4 [non

PI. 2, fig. 6).
? 1956 Spathognathodus cf. inornatus Hass ; Elias : PI. 3, figs. 62, 65 {non PI. 3, figs. 41, 42).
1958 Gnathodus commutatus commutatus Branson & Mehl ; Lys & Serre : 891, PI. 9, figs.
2a, b.

Material. 42 specimens : Holotype X 134, Paratypes X 135-7.

Type locality and horizon. North Crop Sample 3D 14/15.

Range. North Crop CYD 7-3D 22.

Diagnosis. Small gnathodids with elongate blades, and relatively little expanded
posterior platforms, convex in outline, tapering at both ends, and unornamented.

Description. The blade is more or less regular in height or has a gently convex
oral profile in the anterior portion, but for most of the length of the platform the
denticle height decreases uniformly towards the posterior end of the unit. In
mature specimens the anterior blade occupies about half of the total length of the
unit ; it is often deepest at its posterior end, and the oral surface bears about 9 or 10
denticles anterior to its junction with the posterior platform. These denticles tend
to be more or less erect, discrete from about their mid points upwards, and sharply
pointed ; they are strongly laterally compressed and are of sub-equal size, the
largest tending to occur in the posterior portion of the anterior blade. The lateral
faces of the bar are gently convex and the anterior aboral margin is rounded to
bluntly angular ; the anterior edge is straight, and the bar is straight or gently
deflected in a horizontal plane. The blade is continued posteriorly as a central
carina on the platform, the denticles being short, and partly fused ; the total number
of denticles in the blade and the carina is about 22. The posterior platform occupies
the posterior half to two-thirds of the unit ; it is relatively unexpanded laterally
and tapers uniformly at its anterior and posterior ends. It tends to be steep sided,
the lateral faces forming an acute angle below the carina ; one face is often more
strongly laterally expanded than the other. The surface is smooth and no ornamen-
tation is developed, although in some specimens there is a tendency for the appear-
ance of incipient marginal denticulation, similar to that in G. homopunctatus.

The basal cavity is wide and flaring, and is continued anteriorly as a narrow groove
on the base of the anterior blade. The growth of the posterior platform in mature
specimens tends to reduce the angle which its lateral faces form at their junction. In
most specimens its depth is about equal to the height of the carina on its surface.

BRITISH AVONIAN CONODONT FAUNAS 109

Gnathodus ? sp. nov.
Plate 18, figs. 7a-c

Material, i specimen : figured, X 92.

Locality and horizon. North Crop. Sample ZL 8.

Range. North Crop ZL 8.

Description. A gnathodid ? with transversely ridged posterior half of platform ;
anterior part of platform unornamented except for marginal nodes. Base deeply
excavated. Anterior bar unknown.

The anterior blade is broken but the platform is preserved. The carina consists
of a row of low nodes ; in the posterior half of the platform, a row of smaller nodes
runs either side of the carina, with which they fuse to give a series of trinodate
transverse ridges. The inner platform is expanded slightly more than the outer, and
both are unornamented, except for a short marginal row of fused nodes occurring in
the anterior half and diverging posteriorly.

In aboral view the cavity occupies the whole area of the platform and is grooved
along its mid-length.

Remarks. This species is unlike any described gnathodid and does not bear any
obvious phylogenetic relationship to other species.

Gnathodus sp.

Plate 17, figs. 4a-d

Material, i specimen : figured, X 138.

Range. Scotland HOSIE 2A.

Description. A single specimen of Gnathodus appears to be close to G. girtyi, but
differs from it in the character of the lateral denticles of the posterior platform. In
the present specimen the development on the two lateral areas of the platform is
highly asymmetrical, and the platform of the inner-lateral margin, which begins
anterior to the point of origin of that on the outer-lateral margin, is short, and
consists of only three or four fused blunted denticles. Just anterior to its fusion
with the carina, a less conspicuous fused, inner series of lateral denticles is developed
on the outer-lateral platform. These become confluent with the carina just in front
of its posterior termination, but do not reach the posterior end of the carina. The
apron is wide and flaring, and is asymmetrical in both oral and aboral views. In
lateral view the denticles of the anterior blade are sharp and erect, and those of the
carina are also sharply tipped and distinct, standing higher than the lateral denticles
on either side of the platform. The denticles of the inner lateral process form
blunted parapet-like nodes in lateral view. The denticles of the carina decrease
rapidly in size towards the posterior in the posterior half of the platform.

no BRITISH AVONIAN CONODONT FAUNAS

Genus HIBBARDELLA Ulrich & Bassler 1926

1925 Hibbardella Bassler ; 219 (nom. nud.).

1926 Hibbardella Ulrich & Bassler : 37.

Type species. Prioniodus angulatus Hinde 1879.

Description. Ulrich & Bassler established the genus Hibbardella with the type
species Hibbardella (Prioniodus) angulata Hinde for a group of arched blade-like
conodonts in which a striking apical denticle was developed. The whole structure
was bilaterally symmetrical and the apical denticle sharp-edged, erect and greatly
elongated. The denticles of the anterior bar were relatively few in number, widely
spaced and turned slightly inward. Ulrich & Bassler did not mention the character
of the basal cavity, nor the possibility of the development of a denticulated posterior
bar. Topotype material studied by Dr. J. W. Huddle, of which he has kindly
provided us with photographs, shows that both these features are well preserved. A
more or less short stout denticulated posterior bar is developed, and there is a thin
groove-like basal cavity which extends along both the anterior bars and the posterior
bar.

Subsequent authors have erected several genera of essentially similar general form
which have been distinguished on minor morphological differences. These include
Roundya Hass (1953) Ellisonia Muller (1956) and possibly also Diplododella Bassler
(1925). There has been some discussion as to the validity of these and other genera,
especially the genus Trichonodella. The most satisfactory solution to the present
situation seems to be to subdivide the genus Hibbardella into three subgenera, based
on the following characteristics :

1. HIBBARDELLA s.s. arched denticulated conodonts, with a bilaterally
symmetrical anterior bar and a strongly developed apical denticle. The
apical denticle is strongly compressed antero-posteriorly and has sharp

Mam cusp

Denticles

Lateral bar

Posterior bar

Laterol bar

Position of basol cavity

Anterior view

Fig. 23. Hibbardella sp. showing morphological terms used in the text.

BRITISH AVONIAN CONODONT FAUNAS in

lateral edges. The basal cavity is small and restricted to the aboral surface
of the apical denticle, but aboral grooves are developed on both the anterior
and the posterior bars. There is a short stout denticulated posterior bar,
which bears a series of discrete denticles.

Type species. Prioniodns angulatus Hinde 1879.

2. ROUNDYA conodonts of similar overall form to Hibbardella s.s. but charac-

terized by distinctive basal cavities and by the form of the apical denticle.
The basal cavity is relatively much larger than that of Hibbardella, although
it is still confined to the lower surface of the apical denticle. The whole
aboral surface of that denticle is hollowed out, but the cavity does not flare
beyond its basal area. The denticle itself is characterized by its distinctive
cross-section. In its lower half it is broadly sub-circular and robust in form,
the posterior surface having a longitudinal broad concave cavity which is
deepest at the proximal end, and decreases in depth towards the mid-length
of the denticle. The lateral faces of the apical denticle are smooth and
strongly convex, but in their medial areas a conspicuous groove is developed
longitudinally in the lower part. From this a strong lateral costa develops
on each lateral face. In the distal half of the apical denticle it becomes
strongly anterio-posteriorly compressed, but the lateral edges remain sharp,
and the anterior and posterior faces broadly convex.

Type species. Roundya barnettana Hass 1953.

3. HASSOGNATHUS subgen. nov. conodonts whose general form is similar to

Hibbardella, but which are characterized by the fact that the anterior bars
are essentially unexcavated, their aboral surfaces being shallow, concave,
depressions. The basal cavity is conspicuous, but is largely developed
below the posterior bar, although it extends and is continuous with one
below the apical denticle. The apical denticle is usually sub-circular in
cross-section and unornamented. The whole appearance of members of
this subgenus is of a Ligonodina which has developed an additional lateral
bar.

Type species. Trichognathus separata Branson & Mehl 1934.

Subgenus HIBBARDELLA (HIBBARDELLA) Ulrich & Bassler 1926

Hibbardella (Hibbardella) abnormis Branson & Mehl

Plate 31, fig. 6

1940 Hibbardella abnormis Branson & Mehl : 184, PI. 6, fig. 14.

1963 Hibbardella abnormis Branson & Mehl ; Rexroad & Collinson 10, PI. 2, figs. 15, 18, 20, 21.

1965 Hibbardella abnormis Branson & Mehl ; Rexroad & Collinson : 9, PI. 1, figs. 8, 9.

ii2 BRITISH AVONIAN CONODONT FAUNAS

Material. 3 specimens : figured, X 508.
Range. North Crop CYD 7-3D 8.

Description. Rexroad & Collinson (1963) have shown that the holotype of this
species is broken and that the limbs are longer than the original description suggests.

The present specimens are fragmentary, but they show the specific characteristics.
The posterior bar tends to be rather strongly developed, and the lateral bars are
sharply flexed posteriorly.

Hibbardella (Hibbar delta) acuta Murray & Chronic
Plate 25, figs, iga-20

1961 Hibbardella fragilis Higgins : 213, PI. 12, fig. 4, text-fig. 2.
1963 Hibbardella fragilis Higgins ; Bouckaert & Higgins : 17, fig. 3.
1965 Hibbardella acuta Murray & Chronic : 598, PI. 73, figs. 3-5.
Hibbardella higginsi Collinson & Druce in press.

Material. 19 specimens : figured, X 139, X 422.
Range. North Crop 3D 4-3D 17.

Description. The most distinctive features of this species are the greatly
elongated anterior and posterior bars, the relatively slender denticulation and the
lateral twisting of the anterior bars. The apical denticle, although relatively long, is
only about half the length of the anterior bars ; it is slender, with a feebly convex to
flat anterior face and sharp lateral edges ; the posterior part of the face of the apical
denticle is developed into a posterior knife edge, the posterior lateral faces tending to
be rather flat. The anterior bars are long and are longitudinally twisted so that the
denticles tend to originate from the anterior surface. The bars bear up to 10 lateral
denticles which are basally confluent but apically distinct and are more or less com-
pressed anterior-posteriorly. In addition to their longitudinal flexure, the bars are
recurved posteriorly, so that their anterior faces are gently convex. They diverge
from each other at an angle of about 30 °.

The posterior bar is elongated and decreases in depth posteriorly. Its aboral
margin is gently concave, most of the curvature being concentrated near the mid-
point of the unit. Its oral surface bears a series of confluent, but apically distinct,
hindeodellid-type denticles. The larger members of the series tend to increase in
size toward the mid-point of the bar, and then to decrease toward the posterior end.
There are about 8 or 9 main denticles, each separated by two or three smaller
denticles. The denticles are more or less laterally compressed, but tend to have
rather strong convex lateral faces. The lateral faces of the posterior bar are gently
convex. The whole appearance of the posterior bar is strikingly deep and elongated.

Shallow longitudinal slit-like grooves extend along the anterior and posterior bars,
and there is a very small pit below the apical denticle.

BRITISH AVONIAN CONODONT FAUNAS 113

Hibbardella (Hibbardella) milleri Rexroad
Plate 25, figs. 23a-25b

1957 Hibbardella n. sp ? Rexroad : 31, PI. 1, fig. 19.

1958 Hibbardella milleri Rexroad : 18, PI. 2, figs. 13-16.
i960 Hibbardella milleri Rexroad ; Clarke : 6, PI. 1, fig. 6.
1961 Hibbardella milleri Rexroad ; Higgins : PI. 12, fig. 7.

1961 Hibbardella milleri Rexroad ; Rexroad & Burton : 1153, PL 140, figs. 3, 4.

1964 Hibbardella milleri Rexroad ; Rexroad & Furnish : 671, PI. 111, fig. 17.

1965 Hibbardella milleri Rexroad ; Rexroad & Nicoll : 19, PI. 1, fig. 13.

Material. 3 specimens : figured, X 140, X 141, X 142.
Range. North Crop 3D 14/15.

Description. Individual specimens of this species bear a strong resemblance to
those described by Rexroad, but differ from his description in having no denticle
developed anterior to the apical denticle. The most characteristic features of
individuals are the short, deep and obtusely divergent anterior bars, the distal ends
of which are spatulate to sharply pointed. The denticles of the anterior bars are
massive, increasing in size distally and numbering 3 or 4. They are more or less
anteriorly compressed and sharp edged. The apical denticle is massive, elongate,
sub-circular to oval in cross-section ; in some specimens it is very elongate (e.g.
PL 25, fig. 24). In well preserved specimens the apical denticle is sharply pointed at
its distal end, and is sub-circular in cross-section. In the proximal third its posterior
surface is marked by either a very faint groove or a very faint depression. The
posterior bar is short, narrow and deep, with two or three small, isolated denticles on
its oral surface.

The basal cavity is developed as shallow grooves which run along the posterior and
the anterior bars, and the base of the apical denticle is slightly excavated. The
aboral groove does not extend the whole length of the anterior bars, and the posterior
groove decreases in width and depth posteriorly.

Hibbardella (Hibbardella) ortha Rexroad
Plate 25, figs. 22a, b

1900 Prioniodus angulatus Hinde (partim) : 343, PI. 10, fig. 18 (non fig. 19).
non 1926 Hibbardella angulata (Hinde) Ulrich & Bassler : 37, PI. 3, figs. 1-4.
1928 Hibbardella angulata (Hinde) ; Holmes : 11, PL 4, fig. 32.

1958 Hibbardella ortha Rexroad
i960 Hibbardella ortha Rexroad
1961 Hibbardella ortha Rexroad

1964 Hibbardella ortha Rexroad

1965 Hibbardella ortha Rexroad
Hibbardella ortha Rexroad

18, PL 2, figs. 9-12.

Clarke : 6, PI. 1, fig. 7.

Rexroad & Burton : 1153, PL 140, figs. 5, 6.

Rexroad & Furnish : 671, PL 111, fig. 16.

Rexroad & Nicoll : 19, PL 1, fig. 12.

Collinson & Druce in press.

Material. 780 specimens : figured, X 143.

Range. North Crop 3D 10-3D 22.

Description. The present specimens are more complete than those described by

ii 4 BRITISH AVONIAN CONODONT FAUNAS

Rexroad, but they agree in all the essential details with his description. Their most
striking features are the deep and strongly antero-posteriorly compressed anterior
bars, which diverge from each other at an angle of about 130 °. They are relatively
short, and bear on their oral surfaces up to 6 discrete and sharply pointed denticles.
The two nearest the apical denticle and the distal denticle on each bar are small, but
the three intervening denticles are larger and tend to increase in size distally. The
ends of the anterior bar are bluntly spatulate, and the aboral margin is straight to
feebly convex. The anterior face of the apical denticle is convex, the apical denticle
itself being about twice the length of the largest denticle of the anterior bar, slender
and pointed ; it tends to have rather feeble anterior lateral edges in its lower portion,
but becomes sub-oval in cross-section towards its distal end. Both it and the
denticles of the anterior bar tend to stand rather erect to the bar itself and are not
obviously posteriorly recurved, although the denticles of the lateral bar tend to be
inwardly curved towards the apical denticle.

The posterior bar is long, slender, strongly laterally compressed and relatively deep.
It has feebly convex lateral faces, and bears a series of up to 6 crowded, but apically
discrete, laterally compressed, short denticles on its oral surface. A small pit below
the apical denticle extends posteriorly as a faint groove along the posterior bar, and
also along the proximal portions of the anterior bars. The posterior margin of the
apical denticle is sharp-edged. Beneath the apical denticle the posterior-aboral
margin of the anterior bar is excavated by an indented depression to join the basal
margin of the posterior bar.

Hibbardella (Hibbardella) parva sp. nov.
Plate 25, figs. 21a, b

Diagnosis. Hibbardellid with very small, delicate structure ; anterior bars
flexed forwards diverging in vertical plane at a very obtuse angle. At their junction
deeply indented aborally on anterior margin. Posterior bar strong ; apical denticle
elongate, strongly laterally compressed. Basal cavity minute or non-existent.

Material. 5 specimens : Holotype X 144 (figured).

Type locality and horizon. North Crop. Sample 3D 14/15.

Range. North Crop 3D 14/15.

Description. The anterior bars are relatively deep, short and laterally com-
pressed, and each bears about 5 oral denticles. They diverge anteriorly in a
horizontal plane, so that the angle between them in a horizontal plane is about 90 °.
They are little flexed in a vertical plane, and the angle between them is very obtuse.
The aboral surface has a concave general appearance. This anterior curvature is
most obvious in aboral view. It is relatively inconspicuous in oral view, where it is
obscured by the development of the apical denticle, nor is it continued along the
medial and distal parts of the bars which tend to straighten out and lie in a single
plane relative to one another.

Remarks. This species is closest to H. (H.) ortha Rexroad 1958, but it differs in

BRITISH AVONIAN CONODONT FAUNAS 115

the distinctive form of the apical denticle, and in the characteristic angle of the
anterior bars as seen in the vertical plane. In H. (H.) ortha this angle approaches
90 ° but it is nearer 180 ° in H. (H.) parva. H. (H.) ortha also lacks the strong
posterior recurvature of the apical denticle and the denticles of the anterior bar.

Hibbardella (Hibbardella) cf. macrodentata Thomas
Plate 25, figs. i6a-i8c
1949 Hibbardella macrodentata Thomas : 422, PI. 4, fig. 25.

Material. 75 specimens : figured, X 147, X 148, X 146.

Range. North Crop KL 2-ZLA 33, Avon Gorge K3-Z 38.

Description. The apical denticle is tall, laterally compressed and inclined
posteriorly. The anterior arch is deep with each limb curved posteriorly. The
anterior bars diverge at an angle of approximately 90 °, and the aboral edge of the
anterior bars is lower than that of the posterior bar. The denticles of the arch are
isolated, sub-circular and of unequal height. The posterior bar is narrow, long
(though broken in the majority of our specimens) and finely denticulate. All the
denticles are sub-circular and posteriorly inclined. The cavity is minute and
situated beneath the apical denticle.

Remarks. The holotype is broken, but, from Thomas's illustration and description
it would appear that our specimens are very close to H. macrodentata. Although
Thomas describes the posterior bar as blunt and non denticulate, the holotype
(shown in PI. 4, fig. 25) is clearly broken.

Hibbardella (Hibbardella) sp.

Plate 25, figs. 15a, b

Material, i specimen : figured, X 441.
Range. North Crop KL 16.

Description. This specimen is characterized by the massive form of its anterior
bars. The anterior bars are short, deep and strongly downcurved, their oral and
aboral margins being strongly convex in anterior view, although there is a conspic-
uous indentation in the aboral profile below the apical denticle. The strongest
downflexing is in the distal thirds of the bars. The lateral faces of the anterior bars
are convex, and both are characterized by prominent longitudinal ridges developed
just below mid-height, and extending along the length of the bars. The oral surfaces
of the anterior bars bear up to six discrete and rather stout denticles, the largest being
in the medial portions of the bars. They are discrete, more or less rounded in cross-
section, and the larger ones are slightly inflexed towards the apical denticle. Their
length is unknown, but the largest is longer than the depth of the basal bars. The
ends of the bar are spatulate.

The apical denticle is relatively slender, being only slightly greater in width than
the largest of the denticles of the anterior bars. The anterior face is rounded, but

n6 BRITISH AVONIAN CONODONT FAUNAS

the posterior face is blunt and has a median groove. The apical denticle in posterior
view is widest at the oral edge of the bar and tapers uniformly to the tip.

The aboral surface is sharp, being broken only by a small triangular shaped pit
directly beneath the apical denticle.

Subgenus HIBBARDELLA (ROUND Y A) Hass 1953
Type species. Roundya barnettana Hass 1953.

Hibbardella (Roundya) barnettana Hass
Plate 25, figs. 2a-5b

1953 Roundya barnettana Hass : 89, PI. 16, figs. 8, 9.

1957 Roundya barnettana Hass ; Bischoff : 52, PI. 5, figs. 19, 20.

1958 Roundya costata Rexroad : 26, PI. 2, figs. 5-8.

1961 Roundya subacoda (Gunnell) Higgins : 220, PI. n, fig. 13.

1961 Roundya costata Rexroad ; Rexroad & Collinson, PI. 1.

1962 Roundya subacoda (Gunnell) Higgins : 11, PI. 1, fig. 1.

1962 Roundya barnettana Hass ; Collinson, Scott & Rexroad : 12.

Material. 14 specimens : figured, X 151, X 152, X 153, X 154.
Range. North Crop 3D 14/15, Avon Gorge Z 38-C 15.

Description. Individuals of the present species agree closely with the very
detailed description given by Hass (1953 : 89). They are characterized particularly
by the massive apical denticle, with longitudinal grooves and lateral keels which are
very prominent in the proximal portion, and sharp lateral edges which are prominent
in the distal half. There is a conspicuous posterior concave longitudinal depression
in the proximal quarter of the apical denticle, which becomes obsolescent towards the
mid-point. The denticle is strongly recurved in its lower portion, but its distal
portion is straight. The anterior bars are broken in the present specimens, but
appear massive and bear more than two isolated denticles, which are sub-circular in
cross-section, and curve upwards to parallel the apical denticle. The anterior bars
diverge at an angle of about 7o°-8o° in the vertical plane, and the junction between
them is rounded in anterior view. They shallow distally. The posterior bar is
broken in the present specimens, but is clearly massive with flat to gently convex
lateral faces, and has a convex upper surface which bears more than one erect,
massive, sub-circular denticle.

The aboral surface of the apical denticle is deeply excavated and the excavation
continues along the anterior end of the posterior bars.

Hibbardella (Roundya) sp.

Plate 25, fig. 1

Material. 2 specimens : figured, X 423.
Range. North Crop ZLA 32.

BRITISH AVONIAN CONODONT FAUNAS 117

Description. The anterior arch is broken but appears to be formed by aboro-
lateral extensions of the basal cavity. The apical denticle is recurved posteriorly ;
it has a convex anterior margin, lateral keels, and a concave posterior depression,
becoming obsolescent toward the anterior arch. The posterior bar is formed by an
extension of the posterior lip of the basal cavity and bears at least one inclined
denticle.

The basal cavity is large, the aboral region of the apical denticle being completely
excavated.

Subgenus HIBBARDELLA (HASSOGNATHUS) nov.
Type species. Trichognathus separata Branson & Mehl 1934.

Hibbardella (Hassognathus) separata (Branson & Mehl)

Plate 25, figs. I3a-i4

1934 Trichognathus separata Branson & Mehl : 290, PI. 23, fig. 30.

1934 Trichognathus breviolata ? Branson & Mehl : 291, PI. 23, fig. 29.

1938 Trichognathus separata Branson & Mehl ; Branson & Mehl : PI. 33, fig. 42.

1939 Trichognathus separata ? Branson & Mehl ; Cooper : 421, PI. 46, figs. 45, 49.

1944 Trichognathus separata Branson & Mehl ; Branson & Mehl, in Shimer & Shrock : 243,

PI. 93, fig. 72.
1944 Trichognathus separata Branson & Mehl ; E. B. Branson : PI. 32, fig. 42.
1959 Roundya sp. B Hass : 385, PI. 46, fig. 11.

Material. 58 specimens : figured, X 150, X 149.

Range. North Crop KL 19-ZLA 27, Avon Gorge K 21-C 17.

Description. The posteriorly recurved apical denticle is tall and ovate in cross-
section, being thickest at the anterior. The anterior arch is short with the anterior
bars diverging at about 120 °. The bars are narrow, each bearing 3 to 4 short, sub-
circular posteriorly inclined denticles. The posterior bar is relatively long, being
thick at the anterior end, and becoming much thinner over the posterior half, where
it bears a few fine posteriorly inclined denticles.

In aboral view the unit is excavated, with a large cavity occurring beneath the
apical denticle and extending along the posterior bar, but becoming gradually
narrower and ending abruptly. A faint groove runs for a short distance from the
cavity along either limb of the anterior arch.

Remarks. The large basal cavity distinguishes this species from H. macro-
dentata.

Hibbardella (Hassognathus) ? sp.
Plate 31, fig. 3
Material, i specimen : figured, X 319.
Range. Scotland DUN yy.

n8 BRITISH AVONIAN CONODONT FAUNAS

Description. The present specimen is fragmentary but has a very distinctive
appearance. The posterior bar is elongated and tapers towards the posterior end.
The main cusp is strongly recurved and strongly laterally compressed in its distal
half, the proximal half tending to be more rounded. Posterior to it there is a denticle
adding about a third of the total length of the main cusp, and the denticles posterior
to this decrease in size posteriorly. They are short, bluntly pointed and discrete.
The aboral surface of the posterior bar is straight, and the oral surface curves down
to meet it. The two lateral bars are developed well in front to the line of the main
cusp, so that the general appearance of the unit in lateral view resembles that of a
Ligonodina. They are not down-flexed and their aboral margin is in line with that of
the posterior bar. They make an angle of about 90 ° with the posterior bar in a
horizontal plane. They share a single short, but stout, recurved denticle, which lies
directly anteriorly to the main cusp.

The aboral surface of the posterior bar is excavated by a wide elongate depression.
The whole margin tapers towards the posterior end. There is no conspicuous cavity
below the main cusp.

Remarks. One distinctive feature of this specimen is the presence of the denticle
anterior to the main cusp. This might ultimately justify the recognition of speci-
mens of this kind as a new genus, but our present material is inadequate to provide a
full description. Other fragmentary, but different, hassognathids have a much
greater stratigraphic range.

Genus HINDEODELLA Ulrich & Bassler 1926

1925 Hindeodella Bassler : 219 (nom. nud.).

1926 Hindeodella Ulrich & Bassler : 38-41.

Type species. Hindeodella subtilis Ulrich & Bassler 1926.

Hindeodella antecomplex Collinson & Druce
Plate 28, figs. 25, 28
Hindeodella antecomplex Collinson & Druce in press.

Material. 7 specimens : figured, X 157, X 156.

Range. North Crop 3D 4-3D 17.

Description. The present specimens agree closely with the description given by
Collinson & Druce. The most striking features of the specimens are their small size,
the general form of the main denticle, which is relatively massive in relation to the
general size of the unit, being curved posteriorly and inwardly with a very convex
interior antero-lateral face. The denticles of the posterior bar range up to about 10
in number, and the two massive posterior denticles are very prominent in lateral
view. The denticles show a general increase in size posteriorly, as does the depth of
the posterior bar. The aboral margin of the posterior bar is straight, and each of its
aboral lateral surfaces is marked by a flange-like structure. The anterior lateral

BRITISH AVONIAN CONODONT FAUNAS

119

process is short, and bears two oral denticles. It is strongly depressed vertically and
strongly indexed, forming a right angle in its lateral curvature with the posterior bar
when viewed from above. The aboral surface of the unit is excavated by a narrow,
shallow, groove.

Hindeodella brevis Branson & Mehl
Plate 31, fig. 17

1934 Hindeodella brevis Branson & Mehl : 195, PI. 14, figs. 6, 7.

1934 Hindeodella cf. brevis Branson & Mehl : PI. 14, fig. 12.

1956 Hindeodella brevis Branson & Mehl ; Bischoff & Ziegler : 147, PI. 14, figs. 10, 11.

1957 Hindeodella brevis Branson & Mehl ; Bischoff : 26, 27, PI. 6, fig. 24.

Material. 17 specimens : figured, X 514.

Range. Avon Gorge K 2-Z 38, North Crop 3D 14/15-3D 22.

Description. The posterior bar is short, deep, straight and relatively thick at its
oral edge. It bears on its oral surface four or five major denticles, which increase in
size posteriorly. They tend to be straight, strongly biconvex in cross-section, and
only slightly inclined posteriorly. Each is separated by up to 3 smaller denticles,
which are crowded but discrete. The anterior bar is relatively long, and is bent
almost at right angles to the posterior bar. Its oral surface bears up to 7 short
denticles, which decrease in size posteriorly. Each of these major denticles of the
anterior process tends to be separated by a single smaller denticle. The posterior
bar is excavated by a shallow groove in its anterior portion, and this flares somewhat
below the main denticle.

Denticles of
posterior bar

Posterior

Apical denticle

Anterior bar

Posterior bar

Position of basal cavity
A boral edge

Fig. 24. Hindeodella sp. showing morphological terms used in the text.

120 BRITISH AVONIAN CONODONT FAUNAS

Hindeodella cooperi (Elias)
Plate 31, figs. 18, 19

1956 Hamulosodina cooperi Elias : 109, PI. 1, figs. 28, 29.

Hindeodella cooperi (Elias) ; Collinson & Druce in press.

Material. 2 specimens : figured, X 159, X 158.
Range. North Crop 3D 14/15.

Description. The original description of this species is scarcely adequate to
differentiate it from several others of the genus Hindeodella. The most distinctive
features of the present specimens, and also of the specimens shown in Elias' illustra-
tions, are the greatly elongated posterior bar, the more or less subequal character of
the denticulation, and the character of the antero-lateral process. The height of the
denticle is consistent although major denticles can be identified in some parts of the
bar. The anterior-lateral process is short, vertically depressed, slightly laterally
deflected, and bears 1 to 4 denticles anterior to the main denticle, with the whole of
the antero-lateral face undenticulated, and a more or less sharp convex edge.

In lateral view the aboral surface of the unit is straight to gently concave. Its
outer face is flat to steeply convex in the anterior part, but becomes more strongly
convex in the medial and posterior part. The main denticle is not conspicuously
larger than those which lie behind it. The denticles of the main part of the posterior
bar are crowded and fused for most of their length, being slightly inclined posteriorly
and tending to increase slightly in size towards the mid-point of the unit in some
specimens. In other specimens the main denticle is up to twice as large as the main
denticles of the posterior series, and in the latter, the hindeodellid character is more
or less conspicuously developed. The inner lateral face of the unit is flat to gently
convex.

The antero-lateral process makes an angle of about 90 ° with the posterior bar. Its
postero-aboral edge is straight and points vertically, and makes an antero-aboral
angle at the anterior edge of about 45 °. The denticles anterior to the main denticle
tend to be about equal in height to those of the major denticles of the posterior bar,
and curve upwards to lie more or less parallel to the main denticle. The lowermost
anterior edge of the antero-lateral process is undenticulate.

The posterior bar is strongly laterally compressed. Beneath the main denticle
there is a cavity which flares slightly at the edges, and this is extended posteriorly,
and to a less extent, anteriorly as a narrowing groove.

Hindeodella corpulenta Branson & Mehl
Plate 29, figs. i6a-i7c

1934 Hindeodella sp. Branson & Mehl : PI. 14, fig. 15.

1934 Hindeodella corpulenta Branson & Mehl : 281, PI. 22, figs. 32, 33.

1934 Metaprioniodus fr actus Huddle : 58, PL 11, figs. 14, 15.

1934 Ligonodina conidens Huddle : 63, PI. 12, figs. 18, 19.

1938 Ligonodina angulata Branson & Mehl : 142, PL 34, fig. 43.

1939 Ligonodina conidens Huddle ; Cooper : 390, PL 45, fig. 45.

BRITISH AVONIAN CONODONT FAUNAS 121

1944 Ligonodina angulata Branson & Mehl ; E. B. Branson : PL 39, fig. 43.

1947 Hindeodella millerella ? Youngquist & Peterson : 245, PI. 38, figs. 1-5.

1949 Hindeodella cf. Hindeodella corpulenta Branson & Mehl ; Thomas : 408, PI. 1, fig. 4.

1957 Hindeodella ? sp. Lys, Serre & Deroo : 800, PI. 9, fig. 1.

Material. 168 specimens : figured, X 160, X 161.
Range. North Crop KL i-ZLA 33, Avon Gorge K 2-Z 37.

Description. The main denticle is massive with a sub-circular cross-section at
the oral extremity. It is ovate at its base, feebly recurved and posteriorly inclined.
It is about one and a half times as wide as the next largest denticle. The anterior
lateral process is deflected laterally through 90 °, and depressed downward through
90 °. It commonly bears 6 isolated, sub-circular denticles, which increase in size in
the mid part. The posterior bar is massive, laterally compressed and bears about 5
massive, discrete, feebly laterally compressed, posteriorly inclined denticles, the
largest being in the posterior third. No smaller " hindeodellid " denticles are
present. The posterior bar is deflected downward slightly towards the posterior end.

In aboral view the large cavity is situated just anterior to the main denticle, and
extends beneath the anterior lateral process. It is grooved along its mid-length.
The inner lateral face may bear a feeble longitudinal ridge.

Remarks. Most specimens of this species have the posterior bar broken, but the
distinctive anterior lateral process and the basal cavity serve to identify it.

Hindeodella croka Collinson & Druce

Plate 28, figs. 15-17

1957 Hindeodella brevis Branson & Mehl ; Bischoff : 26, PL 6, fig. 24.
1961 Hindeodella brevis Branson & Mehl ; Higgins : PL 10, fig. 14.
Hindeodella croka Collinson & Druce in press.

Material. 7 specimens : figured, X 164, X 162, X 163.

Range. North Crop 3D 9-3D 14/15.

Description. The distinctive elongate form and enormously flexed anterior
lateral process of the species are very distinctive features, and agree in all respects
with the description of Collinson & Druce. There is a tendency in some specimens
for the posterior bar to develop broadly hindeodellid denticulation, but this is not
very clearly defined. In some specimens the anterior lateral process bears up to 8
denticles.

Remarks. A single specimen (PI. 28, fig. 29) is compared with this species,
differing from it in the very strong lateral extension of the inner lateral face of the
unit. It is extended laterally along the whole length of the unit posterior to the
origin of the anterior lateral process, forming a platform-type flange, with a rather
flat, oral surface and a convex to vertical outer lateral face. The relatively incon-
spicuous main denticle is strongly inflexed, downflexed and less strongly recurved.

122 BRITISH AVONIAN CONODONT FAUNAS

Hindeodella hibbardi Collinson & Druce
Plate 28, figs. 18-20

1957 Angulodus walrathi (Hibbard) Bischoff : 17, PI. 5, figs. 44, 45.
1961 Angulodus walrathi (Hibbard) Higgins PI. 10, fig. 16.
Hindeodella hibbardi Collinson & Druce in press.

Material. 22 specimens : figured, X 167, X 168, X 169.
Range. North Crop 3D 11-3D 14/15.

Description. This species of Hindeodella is characterized by a relatively long
anterior lateral process, which is one third to one quarter the length of the posterior
bar, and which is depressed and deflected at the bottom. Immediately anterior to
the main denticle the anterior lateral process is depressed at an angle of about 110°
to the posterior bar. Then, at a distance of about one quarter of its total length from
the main denticle, it is inflexed by lateral twisting, so that the denticles anterior to
this point of inflection point both inwards and also are curved upwards. At a further
point about two-thirds of its length from the main denticle, it is again depressed in a
vertical plane, and the remaining 3 distal denticles of the anterior lateral process are
larger and more strongly recurved than those behind them. The oral surface of the
anterior lateral process bears up to 10 stout denticles, more or less sub-circular in
cross-section, discrete, tending to increase in size distally from the main denticle,
although the most anterior is smaller than those immediately behind it. The
process becomes thinner towards the anterior end, the antero-aboral extremity being
bluntly rounded or plough-like in general form. The proximal end of the anterior
lateral process and virtually the whole length of the posterior bar have conspicuously
and strongly convex lateral faces. The denticles of the posterior bar are strongly
developed, and curve inward, being inclined posteriorly at an angle of about 45°.
The denticles of the main series are each separated by up to 4 smaller, fused, crowded
denticles, which are less than half the length and diameter of those of the larger
series. The posterior third of the unit is slightly depressed vertically and is deflected
laterally.

A very conspicuous aboral groove runs the whole length of the unit, being wide but
rather shallow, and having conspicuous lateral lips. It is reduced in width towards
the anterior and posterior end, and is widest below the main denticle where it is
marked by a more or less conspicuous biconvex pit, both ends of which are relatively
pinched in relation to the rest of the cavity. The outer lateral face is rather less
convex than the inner.

The main denticle is relatively small and inconspicuous in comparison with other
denticles of the series. The whole unit is elongate, but in some specimens the lateral
faces tend to be less convex than others, giving the whole unit a more slender
appearance. In complete specimens the aboral cavity is seen to extend only for
about half the length of the posterior bar.

BRITISH AVONIAN CONODONT FAUNAS 123

Hindeodella ibergensis Bischoff

Plate 28, figs. 22-24, 3°> 3 1

1957 Hindeodella ibergensis Bischoff : 28, PI. 8, figs. 33, 37, 39.

1957 Hindeodella ibergensis Bischoff ; Ziegler in Fliigel & Ziegler : 42, PI. 5, figs. 14, 21.

1957 Hindeodella germana Holmes ; Ziegler in Fliigel & Ziegler : 41, PI. 5, fig. 16.

1958 Hindeodella redunca Stanley : 466, PI. 63, figs. 1-4.

1961 Hindeodella ibergensis Bischoff ; Higgins : PI. 10, fig. 15.

1962 Hindeodella ibergensis Bischoff ; Higgins : PI. 1, fig. 11.

1963 Hindeodella ibergensis Bischoff ; Bouckaert & Higgins : 17, fig. 3.
Hindeodella ibergensis Bischoff ; Collinson & Druce in press.

Material. 37 specimens : figured, X 170, X 171, X 172, X 173, X 174.

Range. North Crop 3D 10-3D 19.

Description. This species includes greatly elongate hindeodellids, with the oral
edge crowded with a series of alternating denticles. The aboral edge is straight to
sinuous. In complete specimens the posterior bar decreases in width progressively
towards the more or less pointed posterior tip. The main denticle is distinct,
incurved and posteriorly deflected through 45 °, being about twice the diameter of the
largest denticles of the main posterior series. The antero-lateral process is short, its
total length being only about one eighth to one tenth that of the posterior bar. Its
postero-aboral edge makes an angle of approximately 90 ° with that of the posterior
bar immediately adjacent to it. Its anterior inner edge is flexed slightly inwards and
there is a series of 3 or 4 recurved, inwardly inclined denticles, which are more or less
discrete pointed, and decrease in size towards the distal end, which is sharply pointed.
Both the degree of " hindeodellid " alternation of the denticles of the posterior bar
and the posterior inclination of the denticles show considerable variation, as also
does the degree of convexity of the lateral faces of the posterior bar, which tends to
increase posteriorly. All denticles of the posterior bar are either very closely spaced
or fused for most of their length, the 3 or 4 which form the posterior end lying almost
horizontally.

Remarks. The only substantial difference between this species and H. cooperi is
the distinctive denticulation of the anterior lateral process, which in the present
species extends as far as the aboral tip of the bar, in contrast to H. cooperi where it is
restricted to the proximal part.

Hindeodella montanaensis (Scott)
Plate 28, figs. 21, 26

1942 Lochreia montanaensis Scott {partim) : PI. 39, fig. 7, PI. 40, fig. 18 (non pi. 39, figs, i,

4, 9 ; PI. 40, figs. 2, 9, 10, 12, 13, 15, 19).
1956 Hindeodella bigeniculata Elias [partim) : 106, PI. 1, figs. 20, 21 {non PI. 1, fig. 16).

1956 Hindeodella mehli Elias : 108, PI. 1, figs. 22-24.

1957 Hindeodella germana Holmes ; Bischoff {partim) : 27, PI. 6, fig. 32, {non PI. 6, fig. 34 =
H. secarata Collinson & Druce).

1958 Hindeodella montanaensis (Scott) Stanley {partim) : 465, PI. 64, figs. 1-5.

i2 4 BRITISH AVONIAN CONODONT FAUNAS

1961 Hindeodella germana Holmes ; Higgins (partim) : PI. 10, fig. 12, (non PI. 10, fig. 13 = //.
secarata Collinson & Druce).
Hindeodella montanaensis (Scott) ; Collinson & Druce in press.

Material. 80 specimens : figured, X 175, X 176.

Range, North Crop 3D 10-3D 19.

Description. Members of this species are slightly constructed hindeodellids,
having a massive main denticle with a very wide base, strongly convex lateral faces,
and being inclined posteriorly at an angle of about 45 °. The denticles on the
posterior bar are minute in comparison with this denticle. They are crowded and
laterally compressed, with sharp anterior and posterior edges, having a hindeodellid
pattern with 2 or 3 smaller denticles between the larger ones. The lateral faces of
the posterior bar are gently to strongly convex. The anterior lateral process is deep
with three confluent denticles near its proximal end, but the distal end, which points
strongly upward and inward, consists of a single fang-like denticle, about half the
width of the main denticle. The basal anterior and posterior edges of the main
denticle are also minutely denticulate. The outer lateral surface of the main denticle
is flat. The aboral surface of the whole unit is excavated by a shallow groove which
flares below the main denticle. The posterior bar is straight and about 5 to 6 times
the length of the anterior bar in the present specimens, but these are broken. One
specimen, which is also broken, shows a tendency for the denticles near the posterior
end of the bar to be relatively larger, about twice as large as most of the denticles of
the posterior bar, although the aboral cavity is little expanded below the main
denticle.

Hindeodella secarata Collinson & Druce
Plate 29, figs, n, 13-15

1957 Hindeodella germana Holmes ; Bischoff (partim) : 27, PI. 6, fig. 34 (non PI. 6, fig. 32==//.

montanaensis) .
1961 Hindeodella germana Holmes ; Higgins (partim) : PI. 10, fig. 13 (non PI. 10, fig. 12 = //.

montanaensis) .
1963 Hindeodella germana Bischoff ; Bouckaert & Higgins ; 17, fig. 3.

Hindeodella secarata Collinson & Druce in press.

Material. 46 specimens : figured, X 184, X 181, X 182, X 183.

Range. North Crop 3D 8-3D 19.

Description. The present specimens agree closely with the description given by
Collinson and Druce. The posterior bar is greatly elongated and tends to taper
towards the posterior end. It is straight to arched, with fine acicular denticles, and
it lacks a well-developed anterior fang. The anterior process is very small, and is
relatively feebly inflexed. The basal groove is conspicuous, but there is no obvious
basal cavity at the anterior end.

BRITISH AVONIAN CONODONT FAUNAS 125

Hindeodella subtilis Ulrich & Bassler
Plate 29, figs. 6a-7b, 9-iob

1926 Hindeodella subtilis Ulrich & Bassler : 39, PI. 8, figs. 17-19.

1927 Hindeodella deflecta Hibbard : 207, fig. 40.

? 1928 Hindeodella germana Holmes : 25, PI. 9, fig. 9.

1928 Hindeodella subtilis Ulrich & Bassler ; PI. 9, figs. 10, 11.

1931 Hindeodella subtilis Ulrich & Bassler ; Cooper : 147, PL 20, fig. 9.
? 1931 Hindeodella pumilla Cooper : 236, PI. 28, fig. 18.

? 1931 Hindeodella subtilita Cooper : 236, PI. 28, fig. 17.

1932 Hindeodella subtilis Ulrich & Bassler ; Bassler : PI. 26, fig. 21.
1934 Hindeodella delicatula Branson & Mehl : 280, PI. 22, fig. 30.

1934 Hindeodella alternidens Huddle : 44, PI. 5, fig. 13 (non PI. 5, fig. 12 — Hindeodella sp.).

1934 Hindeodella angulus Huddle : 44, PI. 5, fig. 15.

1934 Hindeodella aculeata Huddle : 40, PI. 4, fig. 19 (non PI. 4, figs. 20, 21= Hindeodella
sp. cf. H, similis Ulrich & Bassler), PI. 5, figs. 2, 3.

1934 Hindeodella grandis Huddle : 41, PI. 4, fig. 22.

? 1934 Hindeodella laticlavis Huddle : 43, PI. 5, figs. 9, 10.

1935 Hindeodella subtilis Ulrich & Bassler ; Cooper : 309, 310, PI. 27, fig. 27.
1935 Hindeodella germana Holmes ; Cooper : 310, PI. 27, fig. 25.

? 1935 Hindeodella pumilla Cooper ; Cooper : 310, PI. 27, fig. 26.

? 1935 Hindeodella subtilita Cooper ; Cooper : 310, PI. 27, fig. 28.

1938 Hindeodella delicatula Branson & Mehl ; Branson & Mehl, PI. 33, fig. 34.
? 1939 Hindeodella lineata (Pander) Cooper : 389, PI. 46, figs. 28, 31.

1939 Hindeodella delicatula ? Branson & Mehl ; Cooper : 389, PL 46, fig. 33.

1939 Hindeodella acuta Branson & Mehl ; Cooper : 389, PL 46, figs. 15, 23, 29.

1940 Hindeodella moweri Stauffer : 424, PL 58, figs. 2, 10, 11.

1943 Hindeodella subtilis Ulrich & Bassler ; Cooper & Sloss : 170, PL 28, figs. 22, 32, 33.

1943 Hindeodella atteridens Huddle ; Cooper & Sloss : 170, PL 28, fig. 23.

1943 Hindeodella petila Cooper ; Cooper & Sloss : 170, PL 28, figs. 26, 35.

1943 Hindeodella deflecta Hibbard ; Cooper & Sloss : 170, PL 28, figs. 27, 34.

1943 Hindeodella germana Holmes ; Cooper & Sloss : 170, PL 28, fig. 28.

1943 Hindeodella grandis Huddle ; Cooper & Sloss : 170, PL 28, figs. 31, 37, 39.

1943 Hindeodella laticlavis Huddle ; Cooper & Sloss : 170, PL 28, fig. 38.

1945 Hindeodella aculeata Huddle ; Cooper : 613, PL 84, figs. 7, 9.

1945 Hindeodella rotunda Hibbard ; Cooper : 614, PL 84, fig. 8.

1945 Hindeodella grandis Huddle ; Cooper : 614, PL 84, fig. 10.

1945 Hindeodella gracilis Huddle ; Cooper : 614, PL 84, fig. 11.

1945 Hindeodella prioniodon Huddle ; Cooper : 614, PL 84, fig. 12.

1945 Metaprioniodus biangulatus Huddle ; Cooper : 614, PL 84, figs. 13, 14.

1947 Hindeodella aculeata ? Huddle ; Youngquist & Petersen : 244, PL 38, fig. 9.

1947 Hindeodella aculeata Huddle ; Bond : 28, PL 1, figs. 19, 21.

1947 Hindeodella alternata Ulrich & Bassler ; Bond : 29, PL 1, fig. 23.

1947 Hindeodella germana Holmes ; Bond : 29, PL 1, fig. 22.

1947 Hindeodella subtilis Ulrich & Bassler ; Bond : 29, PL 1, fig. 25.

1947 Hindeodella sp. 1 Bond : 29, PL 1, fig. 24.

1947 Hindeodella sp. 2 Bond : 29, PL 1, fig. 20.

x 955 Hindeodella germana Holmes ; Sannemann : 130, PL 2, fig. 45.

1955 Hindeodella deflecta Hibbard ; Sannemann : 129, PL s, fig. 6, PL 5, fig. 8.

1957 Hindeodella germana Holmes ; Lys, Serre & Deroo : 800, PL 8, fig. 7.

1957 Hindeodella deflecta Hibbard ; Lys, Serre & Deroo : 800, PL 8, fig. 6.

126 BRITISH AVONIAN CONODONT FAUNAS

1959 Hindeodella deflecta Hibbard ; Helms : PL 4, fig. 32, PI. 1, fig. 17.

i960 Hindeodella germana Holmes ; Zimmermann : PI. i, fig. 16.

i960 Hindeodella germana Holmes ; Dvorak & Freyer : PI. 1, fig. 1.

1961 Hindeodella germana Holmes ; Budurov : 262, PI. 3, fig. 11.

1962 Hindeodella germana Holmes ; Spasov & Stevanovic : 58, PI. 1, fig. 12.
1962 Hindeodella sp. Winder : 91, fig. 1, 6.

1965 Hindeodella germana Holmes ; Spasov : 86, 87, PI. 1, fig. 10.
1965 Hindeodella similis Ulrich & Bassler ; Spasov : 87, PI. i, fig. 11.

Material. 200 specimens : figured, X 180, X 177, X 178, X 179.
Range. North Crop KL i-ZL 19, Avon Gorge K 3-Z 38.

Description. The main denticle is fairly massive, laterally compressed, biconvex
in cross-section, recurved and posteriorly inclined. The anterior lateral process is
curved inwards at an angle ranging from just a few degrees to nearly 90 °. The
considerably laterally compressed anterior lateral process is finely denticulate, often
with the largest denticles at the anterior. The posterior bar is very thin, compara-
tively deep, and somewhat arched in some specimens, bearing fine, discrete, pointed
denticles. The dentition tends to be cyclic, two major denticles being separated by
three to four minute denticles, all more or less posteriorly inclined. There are up to
14 major denticles on the posterior bar. The posterior termination is composed of
flat lying denticles, inclined at a low angle to the horizontal. It may be aborally
convex (" upswept ") in young forms.

The basal cavity is small, fairly deep, and situated at the anterior end of the apical
denticle.

Remarks. Throughout the Middle and Upper Devonian, and the Tournaisian and
Visean, there occurs a simple hindeodellid with a curved anterior lateral process.
Many different authors have assigned different names to these hindeodellids, depend-
ing on minor variations in such features as the amount of deflection. Within our
collections all types of deflection and various types of dentition can be seen to inter-
grade, and it is probable that all these forms belong to the same variable species.
Further work may show that some of these characteristics may be of specific import-
ance, but at the present time none can be separated.

Hindeodella tenuis Clarke
Plate 28, fig. 27

1900 Ctenognathus obliquus Hinde (partim) : 344, PI. 10, fig. 38.
1928 Hindeodella obliqua Holmes (partim) : 12, PI. 5, fig. 5.
i960 Hindeodella tenuis Clarke : 8, 9, PI. 1, figs. 10, 11.

Material. 4 specimens : figured, X 187.

Range. North Crop 3D 12-14/15.

Description. The present specimens are similar to those described by Clarke.
The posterior bar is elongated, deep, and decreases relatively little in depth towards
its posterior end. The anterior two-thirds is straight and the posterior third gently
down-flexed. The denticles tend to increase in size posteriorly, the most posterior

BRITISH AVONIAN CONODONT FAUNAS 127

being both the largest and the most steeply inclined. The anterior fang is two to
three times the basal width of the largest of the posterior denticles, and is slightly
recurved. The anterior bar is relatively short and the denticles stand erect. The
larger denticles of the posterior bar are separated by only 1 or 2 smaller denticles.
The anterior lateral process is not strongly inflexed.

Hindeodella undata Branson & Mehl

Plate 31, fig. 1

1941 Hindeodella undata Branson & Mehl : 169, PI. 5, fig. 3.

1941 Hindeodella sp. Branson & Mehl : 170, PI. 5, fig. 9.

1953 Hindeodella undata Branson & Mehl ; Hass : 82, PI. 16, figs. 5-7.

1956 Hindeodella undata Branson & Mehl ; Elias : 108, PI. 1, figs. 2, 10.

1956 Hamulosodina bransoni Elias : 108, PI. 1, fig. 4.

1956 Hamulosodina hassi Elias : 108, PI. 1, figs, n, 12.

1 96 1 Hindeodella undata Branson & Mehl ; Higgins : PI. 12, figs, 10, 12.

1963 Hindeodella undata Branson & Mehl ; Bouckaert & Higgins : 17, text-fig. 3.
Hindeodella undata Branson & Mehl ; Collinson & Druce in press, text-fig. 10.

Material. 35 specimens : figured, X 185.

Range. North Crop 3D 4-3D 22.

Description. Specimens of this species are characterized by a relatively long,
deep and straight posterior bar, the aboral margin of which is straight and sharp, and
the sides relatively flat. The oral surface bears a series of alternating denticles which
are acicular in general form, and discrete for the whole of their length. They taper
sharply to a point. Larger denticles tend to be separated by groups of 2 or 3 smaller
ones, which may be laterally offset from the denticles of the main series. The
anterior fang is not greatly larger than the largest of the denticles of the posterior
bar. It makes almost a right angle with the line of the posterior bar and is straight
for the greater part of its length. The anterior inner lateral process is short and
continuously inflexed. It bears one or more needle-like denticles on its oral edge.

Hindeodella sp.
Plate 29, figs. 12a, c

Material, i specimen : figured, X 445.

Range. North Crop ZLA 33.

Description. A single specimen of a small distinctive hindeodellid is illustrated.
The posterior bar is short and relatively deep and bears a series of 5 denticles which
increase in size posteriorly. The inclination of the 4 most posterior is about 45 ° to
the line of the posterior bar, but the most posterior denticle is more strongly inclined.
The apical denticle is rounded in cross-section and the lower part is more or less erect.
The anterior process is sharply down-flexed and continuously inflexed, so that its
distal end makes an angle of about 45 ° with the posterior bar. There is a well-
developed, elongated basal cavity below the fang and the proximal part of the
anterior aboral process.

BRITISH AVONIAN CONODONT FAUNAS

Hindeodella sp. nov.
Plate 28, figs. 14a, b

Material, i specimen : X 186 (figured).

Type locality and horizon. North Crop. Sample 3D 14/15.

Description. A single specimen is tentatively regarded as a new species of
Hindeodella, although it may be a pathologic form. It is characterized by a con-
tinuously recurved, hooked anterior lateral process and a very sinuous posterior bar.
The general appearance of the unit is of a question mark, with the posterior end
forming the base of the question mark. The posterior bar is shallow, being about
equal in depth to the smaller series of denticles developed on its oral surface. Its
aboral edge is strongly convex in its anterior half and concave in its posterior half, so
that the whole effect is of a sinuous development. Its outer lateral face is strongly
convex in the anterior half, and flat to gently convex in the posterior part.

The oral surface of the posterior bar bears a series of about 18 denticles of variable
size, which show no regular alternation. They are basally confluent but apically
distinct, and are sharply pointed, with sharp anterior and posterior edges. Those
near the posterior end tend to be more strongly inclined posteriorly than those in the
anterior part, which are only gently inclined posteriorly. Although these denticles
show no regular alternating arrangement, some of them are conspicuously larger than
others and these are developed at variable intervals. The largest of them are about
twice the length of the smallest, and they show a broad tendency to increase in size
posteriorly. Their total number is probably greater than 18 as the present specimen
is broken. The main denticle is about equal in size to the largest denticles of the
posterior bar, being sharply recurved and incurved. Immediately posterior to it the
aboral surface of the posterior bar is flat, although its general structure is still broadly
convex.

The antero-lateral process consists of two more or less distinct parts. There is a
sharply up-flexed part, in which the aboral edge of the process makes an angle of
about 70 ° with the aboral edge of the posterior bar immediately posterior to the main
denticle. It is not greatly flexed to the natural plane, however. On the anterior end
of this are two conspicuous denticles, which are incurved, as well as recurved, so that
their " anterior and posterior " edges are in fact lateral in position. They are greater
in size than the main denticle and exceed the size of the largest denticles of the
posterior bar by about a half. The aboral surface of the unit is excavated by a very
thin groove.

Genus HINDEODUS Rexroad & Furnish 1964

1964 Hindeodus Rexroad & Furnish : 671
Type species. Trichonodella imperfecta Rexroad.

BRITISH AVONIAN CONODONT FAUNAS 129

Hindeodus alatoides (Rexroad & Burton)
Plate 31, figs. 7, 10.

1961 Falcodus ? alatoides Rexroad & Burton : 1152, PI. 140, fig. 8.

1964 Hindeodus alatoides (Rexroad & Burton) Rexroad & Furnish : 67, PI. in, figs. 18, 19.
1 96 1 Falcodus (?) n. sp. Rexroad & Collinson : PI. 1.

1965 Hindeodus alatoides (Rexroad & Burton) Rexroad & Nicoll : 20, PI. 2, fig. 10.

Material. 3 specimens : figured, X 193, X 192.

Range. Scotland HOSIE 2B-2C.

Description. The present specimens are distinguished by the short laterally
flexed anterior limb, which is deepest and bears the largest denticles distally. The
apical denticle is only slightly inclined posteriorly and its distal portion is straight.
It is little compressed laterally. The posterior bar is straight and elongated, its
length being about three times that of the anterior bar. The denticles are short,
discrete and bluntly pointed, tending to alternate in size and standing more or less
erect to the posterior bar in some specimens, but being slightly inclined in others.
The apical denticle is conspicuously elongated, and has a basal width of up to three
times that of the adjacent denticles. The denticles of the posterior bar tend to
increase in size posteriorly. The aboral cavity is relatively small.

Hindeodus imperfectus (Rexroad)
Plate 31, fig. 8

1957 Trichonodella imperfecta Rexroad : 41, PI. 4, figs. 4, 5.

1958 Trichonodella imperfecta Rexroad ; Rexroad : 26, PI. 4, fig. 6.
1961 Elsonella ? imperfecta (Rexroad) Rexroad & Collinson : 6.

1961 Elsonella ? imperfecta (Rexroad) Rexroad & Burton : 1152, PI. 141, fig. 1.

1964 Hindeodus imperfectus (Rexroad) Rexroad & Furnish : 672, PI. 111, figs. 13, 14.

1965 Hindeodus imperfectus (Rexroad) Rexroad & Nicoll : 20, PI. 2, fig. 11.

Material, i specimen : figured, X 194.

Range. Scotland HOSIE 2B.

Description. The present specimens are generally fragmentary, but they show

Apical denticle

Posterior
Anterior bor

aboral
Outer lateral face margin Posterior bar

Lateral view

Fig. 25. Hindeodus sp. showing morphological terms used in the text.

130 BRITISH AVONIAN CONODONT FAUNAS

the general symmetry of this species, a feature that is so striking that it led Rexroad
in his initialdescription to assign it to the genus Trichonodella. The denticles tend to
increase in size towards the distal third of the bars, and the apical denticle tends to
stand erect between the converging denticles of the anterior and posterior bars.
There is a feeble basal flange below the apical denticle.

Hindeodus sp.

Plate 22, figs. I7a-20b
1964 Hindeodus sp. Rexroad & Furnish : 672, PI. m, fig. 11.

Material. 10 specimens : figured, X 189, X 191, X 188, X 190.

Range. Scotland HOSIE 2A-2B.

Description. Certain of the present specimens, although showing minor varia-
tions in form, are obviously closely related to one another. These specimens possess
a short, deep, posterior bar which has a straight aboral margin in lateral view. The
bar is slightly flexed inwards longitudinally and its oral surface bears at least 10
confluent denticles, only their apices being discrete and bluntly pointed. They are
inclined gently posteriorly and are more or less of uniform size. The apical denticle
is about twice as long as the largest denticles of the rest of the bar. It is basally
confluent to those on either side of it and has sharp anterior and posterior edges and a
strongly biconvex cross-section. The anterior bar is shorter than the posterior, and
is gently concave basally in lateral view. Its oral surface bears a series of about 5
denticles, similar in form to those of the posterior bar, which tend to decrease in size
anteriorly and which are recurved so that they he sub-parallel to the apical denticle.
It makes an angle of about 90°-iio° with the posterior bar. The denticles of the
anterior bar tend on the whole to be rather broader than those of the posterior. The
inner lateral face of the anterior bar is gently concave. In outer lateral view the
whole unit is seen to be gently arched inwardly and its outer lateral face is flat to
gently convex. There is a slightly expanded cavity below the apical denticle and
very fine longitudinal grooves extend along the lengths of the two bars.

Genus KLADOGNATHUS Rexroad 1958

1958 Kladognathus Rexroad : 19 {pro Cladognathus Rexroad 1957, 28 non Burmeister 1847).
1961 Cladognathodus Rexroad & Collinson : 6 (abs. syn.).

Type species. Cladognathus prima Rexroad.

This genus was first described by Rexroad in 1957 under the name Cladognathus, a
name later found to be a homonym of one used by Burmeister in 1847. The name
Kladognathus was proposed by Rexroad 1958, as a substitute. Rexroad & Collinson
(1961 : 6), however, changed this to Cladognathodus because they suggested that the
replacement of a letter " C " by a letter " K " did not represent a valid name change
under the rules of nomenclature. Article 56A of the International Code makes it
clear, however, that a difference of even one letter in the spelling of generic names
represents a valid distinction between them. The name Kladognathus Rexroad 1958

BRITISH AVONIAN CONODONT FAUNAS 131

is thus the senior and correct name for the genus, and Cladognathodus Rexroad &
Collinson 1961 is a junior synonym. We are grateful to Dr. Curt Teichert for
pointing this out to us (see also Mound 1965).

Kladognathus clarensis Collinson & Druce
Plate 23, figs. ia-2b
Kladognathus clarensis Collinson & Druce (in press).

Material. 3 specimens : figured, X 195, X 196.
Range. North Crop 3D 10-3D 23.

Description. In lateral view this species resembles the genus Metalonchodina.
Its most striking feature is the greatly enlarged, laterally compressed denticle which
comprises most of the posterior bar. This is inclined posteriorly but the curvature
may be more or less continuous, or it may be chiefly confined to the base, with the
upper part of the denticle having straight anterior and posterior edges. The inner
lateral face tends to be rather more convex than the outer. The posterior aboral
termination is more or less sharply pointed.

The fang is relatively small in comparison with the posterior denticle. It is
slender, posteriorly continuously recurved, and has sharp anterior and posterior
edges. The anterior bar consists of 1 to 3 denticles and the anterior aboral margin is
spatulate in form with the anterior aboral angle being rounded. In multidenticulate
anterior bars the most anterior denticles tend to be more or less erect, but the more
posterior ones tend to be recurved.

The lateral process is short and bears at least one oral denticle. The whole unit
tends to be laterally deflected, the outer lateral face tending to be concave. The
aboral surface below the main denticle on the posterior bar is broad, and has a
conspicuous flattened basal surface. It consists essentially of an inverted basal
cavity, with a median groove which is continued along the anterior bar. All of the
three present specimens have a short, laterally compressed, inconspicuous denticle
lying between the fang and the main denticle of the posterior bar.

posterior
Fong

Anterior Bar /,/ Posterior denticle

Aboral margin
Fig. 26. Kladognathus sp. showing morphological terms used in the text.

132 BRITISH AVONIAN CONODONT FAUNAS

Remarks. The present specimens show strong resemblances to those described
by Clarke (i960) as Ligonodina complectens. Rexroad & Collinson (1963 : 13)
transferred Clarke's specimens to the genus Magnilaterella. The present specimens
differ from those of Clarke chiefly in the presence of an anterior bar, and it is this
distinctive feature which justifies their inclusion in the genus Kladognathus.

Kladognathus macrodentatus (Higgins)
Plate 23, figs. 3-6

1961 Lambdagnathus macrodentata Higgins : 214, PI. 12, figs. 1-3, text-fig. 3.

1963 Lambdagnathus macrodentata Higgins ; Bouckaert & Higgins : 17, fig. 3.

Kladognathus macrodentata (Higgins) Collinson & Druce (in press).

Material. 15 specimens : figured, X 197, X 198, X 199, X 200.
Range. North Crop 3D 10-3D 22.

Description. This species is characterized by a long arched posterior bar which
bears characteristically hindeodellid denticulation on its oral surface. The larger
denticles are separated by 1 or 2 smaller denticles, which are basally confluent but
apically discrete. In well preserved specimens the major denticles of the series are
very long, the largest, in the middle of the posterior blade, commonly being about
three times the depth of the posterior bar.

The short laterally compressed anterior bar is downflexed, but lies in the same
plane as the posterior bar. Its anterior aboral margin is bluntly spatulate. There
tend to be 2 or 3 small denticles in front of the apical denticle. The lateral bar is
short, deeply arched, laterally compressed, and strongly deflected posteriorly, making
an angle of 25°-45° with the arcuate posterior bar when seen in oral view. The
lateral bar carries 1 or 2 stout, discrete denticles on its oral surface. The aboral
margin of the entire unit is excavated by a shallow groove.

Kladognathus mehli (Rexroad)
Plate 31, fig. 15

1957 Cladognathus mehli Rexroad : 29, PI. 1, figs. 11, 12.

1958 Kladognathus mehli (Rexroad) Rexroad : 19, PI. 3, fig. 5.

1965 Kladognathus mehli (Rexroad) Rexroad & Nicoll : 20, 21, PI. 1, fig. 7.

Material. 3 specimens : figured, X524.

Range. North Crop 3D 14/15.

Description. This species is characterized by a very large, laterally compressed
recurved fang, strong discrete denticles on the anterior and posterior bars, relatively
strong curvature on the anterior and posterior bars, and a conspicuous attachment
scar on the inner lateral face at the anterior end of the posterior bars. Our specimens
agree closely with those illustrated by Rexroad.

BRITISH AVONIAN CONODONT FAUNAS

133

Genus LIGONODINA Ulrich & Bassler 1926

<,ssler : 218 (nom. nud.).
rich & Bassler : 12, 13.

Type species. Ligonodina pectinata Ulrich & Bassler 1926.

1925 Ligonodina Bassler : 218 {nom. nud.).

1926 Ligonodina Ulrich & Bassler : 12, 13.

1934
1934
1934
1939
1943
1944

non 1944

1947

1949

non 1949

non 1964

Ligonodina beata nom. nov.

Plate 26, figs. 4~6b

Ligonodina delicata Branson & Mehl : 199, PL 14, figs. 22, 23.

Ligonodina delicata Branson & Mehl ; E. R. Branson : 328, PI. 27, fig. 3.

Ligonodina sp. Huddle : 62, PI. 12, fig. 8.

Ligonodina delicatula Cooper : 390, PI. 45, figs. 50, 60, 61.

Ligonodina tenera Cooper & Sloss : 174, PI. 29, fig. 34.

Ligonodina delicata Branson & Mehl

PI. 93. fig- 74-

Ligonodina delicata Branson & Mehl ;

sp).

Ligonodina delicata Branson & Mehl

Ligonodina delicata ? Branson & Mehl ;

Ligonodina delicata Branson & Mehl ;

Branson & Mehl in Shimer & Shrock :

241,

E. B. Branson : PL 26, fig. 23, (=Palmatolepis

Miller & Youngquist : 509, 510, PL 73, fig. 12.
Thomas : 408, 411, PL 4, fig. 22.
Thomas : PL 3, fig. 41, (=Ligonodina sp.).
Bergstrom : 28, text-fig. 12. Bergstrom

non 1964

(1964, 28) has demonstrated that Phragmodus delicatus Branson & Mehl, 1933, 123,
PL 10, fig. 22) should be regarded as a species of Ligonodina. The name for this
species, therefore, has precedence over that of Ligonodina delicata Branson & Mehl
(1934, z 99) an< 3 the latter species becomes a junior homonym of the former. In
this case, it is necessary to select a new name, and we have selected the name
Ligonodina beata. The holotype is University of Missouri Catalogue No. C. 243-4
(Branson & Mehl 1934 : z 99)-
Ligonodina delicata Branson & Mehl ; Budurov & Tschurner : PL V, figs. 23a, b.

Material. 361 specimens : figured, X 202, X 203, X 201.
Range. North Crop KL 19-ZLA 21, Avon Gorge K 3-C 25.

Description. A fragile unit with a slender main denticle which has a sub-circular
cross-section. The main denticle is recurved posteriorly at 45 °. The anterior-
aboral process originates immediately anterior to the main denticle, and commonly
bears 3 or 4 isolated, discrete, sub-circular denticles, which are posteriorly inclined.
The posterior bar is fairly long and rarely preserved. It bears up to 6 isolated
laterally compressed denticles, which are posteriorly inclined, and tend to increase in
size posteriorly.

In aboral view, the anterior portion of the posterior bar is excavated, the deepest
excavation being beneath the main denticle ; the cavity extends inverted beneath
the anterior aboral process. The cavity is grooved, the groove running some way
along the posterior bar and the complete length of the anterior aboral process.

Remarks.
& Mehl.

Our specimens agree very closely to the holotype described by Branson

134 BRITISH AVONIAN CONODONT FAUNAS

Ligonodina levis Branson & Mehl
Plate 26, figs. 15a, b, I7a-i9b

1941 Ligonodina levis Branson & Mehl : 185, PI. 6, fig. 10.

1949 Ligonodina sp. Youngquist & Miller (partim) : 620, PI. ioi, figs. 12 & 13 only.

1957 Ligonodina levis Branson & Mehl ; Bischoff : 30, PI. 5, figs. 8, 9, PI. 6, fig. 25.

1957 Ligonodina obunca Rexroad : 32, PI. 1, figs. 22, 23.

1958 Ligonodina obunca Rexroad ; Rexroad : 21, PI. 3, figs. 7, 8.

1961 Ligonodina levis Branson & Mehl ; Rexroad & Burton : 1154, PI. 141, figs. 7, 8.

1963 Ligonodina levis Branson & Mehl ; Thompson & Goebel : 11, fig. 3.

1963 Ligonodina levis Branson & Mehl ; Rexroad & Collinson : 11, PI. 2, figs. 24, 25.

1964 Ligonodina levis Branson & Mehl ; Rexroad & Furnish : 672, PI. 111, fig. 381.

1965 Ligonodina levis Branson & Mehl ; Rexroad & Nicoll : 21, PI. 2, fig. 24.

Material. 25 specimens : figured, X 204, X 205, X 206, X 207.
Range. North Crop CYD 6-3D 14/15, Avon Gorge Z 38-D 26.

Description. Rexroad's original description of this particular species was rather
generalized, but the distinctive features seem to be the massive and rather rounded
main denticle, which is continuously recurved, especially in its lower part, so that its
distal portion makes an angle of about 45 ° with the posterior bar. The distal
portion is not greatly laterally compressed, although it has sharp anterior and
posterior edges ; the lateral faces are themselves strongly convex. The posterior
edges become obsolescent towards the proximal end. The outer lateral aboral
surface is expanded slightly laterally, but has a conspicuous flange-like structure
developed along it, which slopes towards the aboral cavity. The proximal inner
portion of the main denticle is very strongly convex.

The posterior bar is of unknown length but is more or less quadrate in cross-section,
with a broad aboral edge. It bears at least one, stump-like denticle, which is well
separated from the base of the main denticle. The antero-aboral surface of the main
denticle tends to be rather rounded, and in oral-outer lateral view extends below the
main level of the denticle in a rather bluntly pointed termination. The main
denticle extends in a continuous curve downward to form the inner anterior aboral
process. The aboral surface of this process lies at an acute angle, often as small as
45 , to the posterior bar. Its oral surface bears up to 5 large denticles, of which
those at the anterior end tend to be very large. They are straight to slightly curved

Moin denticle

Inner-loterol
lamina

Anterior aboral
process

Posterior denticles

Posterior bar

Fig. 27. Ligonodina sp. showing morphological terms used in the text.

BRITISH AVONIAN CONODONT FAUNAS 135

and are directed inwards and upwards. The denticles are discrete and more or less
sub-circular in cross-section.

The antero-aboral process decreases in thickness towards the distal end. The
aboral surface is characterized by thick, aborally directed, lip-like, flange structures
along the lateral edges of both the posterior bar and the antero-aboral process.
There is a pit-like cavity below the main denticle and there are longitudinal grooves
along the aboral surface of the posterior bar and the antero-aboral process. These
decrease in width towards the distal end of the process.

Ligonodina magnilaterina sp. nov.
Plate 26, figs. 8a-nb

Derivation of name. From the resemblance of the species to the genus Mag-
nilaterella.

Diagnosis. Ligonodinid with a denticle situated anterior to main denticle,
forming continuation of denticle series of posterior bar. Anterior denticle only
slightly smaller in size than main denticle, though tending to be rather more slender
in general form ; lying at junction of antero-aboral process and posterior bar.

Material. 6 specimens : Holotype X 211, Paratypes (all figured) X 208, X 209,
X 210.

Type locality and horizon. Scotland Sample HOSIE 2C.

Range. Scotland HOSIE 2C.

Description. The main denticle is strong, the base being strongly developed
anteriorly and posteriorly. It is of unknown length, sub-circular in cross-section in
the lower part. The main denticle is recurved in its lower part, the inner and outer
lateral faces being strongly convex. The posterior margin of the main denticle is
extended to form the oral surface of the posterior bar. This bar is of unknown
length, but is deep in its anterior part and bears at least 4 discrete denticles, which
are only slightly laterally compressed and of variable size. It is possible that they
may be arranged in a cyclic pattern.

On the anterior face of the main denticle a thickened denticle is developed at the
junction of the anterior denticle and the antero-aboral process. This denticle is
distinct from those of the antero-aboral process and in inner lateral view it seems to
represent a continuation of the posterior bar. In outer lateral view it may be seen to
be recurved inwardly at its base ; its anterior face is strongly convex with sharp
lateral edges. It is recurved slightly posteriorly to lie sub-parallel to the main
denticle, and also slightly inwardly. It is fused at the base to the main denticle and
arises from it at a strongly convex junction. It is long and slender, being sharply
pointed at its distal end and is about half the diameter of the main denticle. The
other denticles of the anterior aboral process, which number at least three, are
discrete, sub-circular in cross-section with poorly defined, but rather sharp, lateral
edges. They tend to decrease in size distally. The anterior aboral process appears
to be relatively short, although none of the present specimens is complete. It is

136 BRITISH AVONIAN CONODONT FAUNAS

strongly recurved in a vertical plane and its proximal aboral surface makes almost a
right angle with the posterior bar. It is also strongly recurved with respect to the
aboral surface of the posterior bar. The curvature of the anterior edge of the
process is in line with the anterior denticle and not with that of the main denticle.
It makes an angle of about 45 ° with the posterior bar in a horizontal plane.

The aboral surface is excavated by a very shallow and rather inconspicuous
groove, which runs along at least the anterior part of the posterior bar and is con-
tinuous with a similar cavity below the anterior aboral process. The cavity below
the main denticle is very narrow and not over-deep.

Remarks. This species is distinguished from all other ligonodinids by the form
and the position of the denticle anterior to the main denticle. In this feature it
approaches, but does not reach, the typical forms of the genus Magnilaterella
Rexroad and it is also reminiscent to some extent of some Ordovician species of the
genus Phragmodus.

Ligonodina osborni sp. nov.
Plate 26, figs. ia-2c

Derivation of name. This species is named in honour of Mr. S. Osborn of the
Geology Department, University College of Swansea.

Diagnosis. Ligonodinid with a conspicuous continuously recurved main denticle,
strongly biconvex in cross-section, with feeble anterior and posterior edges, distal
portion not preserved in present specimens. Posterior bar of unknown length,
strongly depressed in vertical plane, bearing on oral surface series of isolated,
posteriorly inclined denticles, appearing to increase in size posteriorly ; separated by
distance about equal to their basal width. A short, sinuous, sharply flexed, pointed
anterior aboral process, bearing 2 isolated denticles ; proximal larger than distal.

Material. 6 specimens : Holotype X 212, Paratype X 213 (both figured).

Type locality and horizon. North Crop. Sample 3D 14/15.

Range. North Crop 3D 8-3D 14/15.

Description. The main denticle is large and strongly recurved, its whole
anterior edge being strongly convex, and its posterior strongly concave. The distal
portion is of unknown form but the basal part is biconvex in outline, with only
inconspicuously developed anterior and posterior edges. It is extended posteriorly
into a strongly arched posterior bar, the aboral edge of which is concave. Its lateral
faces are flat or only very feebly convex, and there is a sharp basal ledge developed
along its preserved length. Its oral surface bears at least 3 isolated, posteriorly
inclined, denticles, which are biconvex in cross-section, and the third of which is
larger than the first or second. These are inclined at an angle of about 45 ° to the
posterior bar, and are separated by a distance about equal to their basal width.

The antero-aboral process makes an angle in a vertical plane of about 90 ° with the
line of the posterior denticle, so that its denticles point directly inwards and also a
little posteriorly, because of their recurvature. It bears at least 2 isolated denticles,

BRITISH AVONIAN CONODONT FAUNAS 137

which are biconvex in cross-section and have inconspicuous lateral edges. They are
separated by a great distance and the distal is the smaller of the two. The whole
anterior aboral surface tapers rapidly towards its distal tip ; although its depth
remains constant, its width decreases conspicuously. Its distal tip is also flexed
gently forward. In lateral view the most striking feature of the anterior aboral
process is that it is so recurved posteriorly that it has an angular protruding junction
with the base of the main denticle. It is then flexed forwards so that the whole
appearance of the combined aboral process and anterior denticle is of a feebly sinuous
line. In outer lateral view the flexure and decrease in width of the anterior aboral
process are conspicuous features. The lip below the main denticle is also strikingly
developed in lateral view, the whole inner lateral face of the unit being very feebly
convex. In aboral view the unit is greatly expanded below the main denticle and
there is a conspicuously flattened, but sloping, surface which is deeper on the outer
lateral side. It narrows rapidly towards the posterior bar, which is excavated by a
relatively deep, rounded groove. The main basal cavity is restricted to the median
part below the main denticle. The anterior aboral process also has a very wide
aboral surface, which is only partly excavated, but it narrows rapidly towards a
pointed distal end and is somewhat twisted in aboral view. It is deflected to make
an angle of 90 ° in a vertical plane with the main denticle.

Ligonodina roundyi Hass

Plate 26, figs. I3a-i4b, i6a-c

1926 Prioniodus sp. A. Roundy : 11, PI. 4, fig. 9.

1926 Prioniodus sp. C. Roundy : 11, PI. 4, fig. 11.

1953 Ligonodina roundyi Hass : 82-83, PI. 15, figs. 5-9.

1956 Ligonodina roundyi Hass : Elias: 126, PI. V, figs. 10-14.

1958 Ligonodina roundyi Hass ; Rexroad : 21, PI. 3, figs. 1-4.

1961 ^Ligonodina typa (Gunnell) Higgins : 220, PI. 11, fig. 6.
Ligonodina roundyi Hass ; Collinson & Druce (in press).

Material. 24 specimens : figured, X 214, X 215, X 216.
Range. North Crop 3D 14/15.

Description. This species of Ligonodina is characterized by a massive and
elongate main denticle and a strongly developed antero-aboral process. The
posterior bar is relatively slender in comparison with the proportions of the two
latter elements.

The main denticle is greatly elongated, and more or less strongly expanded
anteriorly and posteriorly at its base. It is sharply pointed and in its distal half it is
very strongly laterally compressed, the anterior and posterior edges being sharp and
the lateral faces feebly convex. The curvature of the main denticle is concentrated
in the proximal third, the remainder being straight. It is also twisted in the vertical
plane, so that the anterior edge points inwardly ; in its outer aboral portion the main
denticle is strongly rounded, but the corresponding inner lateral face is flat to feebly
concave. Along the inner anterior margin a relatively strong and sharp keel is

138 BRITISH AVONIAN CONODONT FAUNAS

developed, which is the main anterior edge of the denticle ; it extends aborally as a
sharp ridge, which forms the edges of the denticles of the anterior aboral process.
The posterior face of the main denticle tends to become rather depressed and may
develop a low concave depression.

The antero-aboral process points vertically downwards, making an angle of
8o°-ioo° with the posterior bar. It is not deflected out of line with the main denticle
to any great extent. The oral surface of the anterior aboral process bears up to 6
denticles, the largest of which occurs in the medial portion ; the denticles are
strongly compressed anteriorly and posteriorly in their distal portions. Though
their bases are sub-circular in outline, they have strong lateral edges and are recurved
inward and upward ; they are discrete but relatively closely spaced. The posterior
bar is relatively slender and bears at least 2 (the present specimens are all broken)
discrete, sub-circular, widely spaced, feebly posteriorly inclined, bluntly pointed,
peg-like denticles.

The outer lateral face of the main denticle is strongly flared and the edges of the
cavity are thick ; there is a deep, but limited lip below the main denticle which is
extended along the aboral anterior process as a conspicuous longitudinal groove on
the aboral surface ; it is also extended for at least some distance along the posterior
bar.

The width and depth on the antero-aboral process decrease towards the distal
extremity, which is bluntly rounded. The posterior bar is more or less quadrate in
cross-section.

Ligonodina tenuis Branson & Mehl
Plate 31, figs. 4, 16

1941 Ligonodina tenuis Branson & Mehl : 170, PI. 5, figs. 13, 14.

1949 Ligonodina sp. Youngquist & Miller (partim) : 620, PI. 101, fig. 11 only.

1956 Ligonodina tenuis Branson & Mehl ; Elias : 126, PI. 5, figs. 4, 5.

1957 Ligonodina sp. Rexroad : 33, PI. 1, figs. 20, 21.

1957 Ligonodina hamata Rexroad : 32, PI. 1, figs. 24, 25.

1958 Ligonodina hamata Rexroad ; Rexroad : 21, PI. 3, figs. 9-14.
i960 Ligonodina tulensis (Pander) Clarke 11, PI. 2, fig. 4.

1961 Ligonodina obunca Rexroad ; Higgins : PI. 11, fig. 9.

1961 Ligonodina hamata Rexroad ; Rexroad & Burton : 1154, PI. 141, figs. 5, 6.

1964 Ligonodina tenuis Branson & Mehl ; Rexroad & Furnish : 672, PI. in, fig. 40.

1965 Ligonodina tenuis Branson & Mehl ; Rexroad & Nicoll : 22, PI. 2, figs. 12-15.

Material. 15 specimens : figured, X 320, X 321.

Range. North Crop 3D 8-3D 22.

Description. Specimens of the species, though generally fragmentary, display
the distinctive features of the holotype. They have a characteristically strongly
developed long, slender main denticle, which is continuously recurved, although the
distal portion tends to be rather straight : the lateral faces are convex to flat, and
the aboral margin tends to bear a more or less conspicuous ledge. The denticles of
the posterior bar are relatively small in comparison with the size of the unit.

BRITISH AVONIAN CONODONT FAUNAS 139

Ligonodina tulensis (Pander)
Plate 31, fig. 9

1856 Prioniodus tulensis Pander (partim) : 30, tab. 2a, fig. 19 only.

1900 Prioniodus tulensis Pander ; Hinde (partim) : 343, PI. 9, fig. 15 only.

1928 Prioniodus tulensis Pander ; Holmes (partim) : 22, PI. 3, fig. 22 only.

Material. 6 specimens : figured X 328.

Range. North Crop CYD 6-CYD 7.

Description. The present specimens are fragmentary but they display most of
the features described by Clarke. The main denticle tends to be rather large in
comparison with the size of the posterior bar ; its lateral faces are flat to gently
convex, and in its lower portion the anterior and posterior edges tend to be blunted.
The denticles of the posterior bar are relatively small, and are discrete. The anterior
aboral process is strongly recurved laterally, and is also twisted, so that the denticles
are directed anteriorly. Its distal end makes a right angle in a horizontal plane with
the posterior bar. The denticles of the process tend to be rather larger than those
of the posterior bar.

Ligonodina sp. A

Plate 26, figs. 3a-c

Material, io specimens : figured, X 217.

Range. North Crop ZLA 32-ZLA 33.

Description. All the present specimens are broken, but the species appears to be
a ligonodinid with a greatly excavated main denticle. The main denticle itself is
massive, sub-circular in cross-section, with a sharp lateral costa developed in line
with the anterior aboral process. The antero-aboral process is broken, but the
posterior bar can be seen to be short, bearing three tall isolated denticles, and having
its aboral side grooved.

Remarks. The overall appearance of this species is of a Roundya with only one
limb of the anterior arch developed. Youngquist, Miller & Downs (1950 : 527)
illustrate and describe similar forms as Ligonodina? sp. Our material is too frag-
mentary for a specific designation but it would appear that the two forms may be
conspecific.

Ligonodina ? sp.
Plate 26, fig. 7

Material, i specimen : figured, X 218.

Range. North Crop ZLA 11.

Description. This appears to be a pathological form of L. beata. There is a
secondary lateral process developed on the inner side of the posterior bar and it bears
one low node. The angle of the process, and its inclination toward the posterior, are
parallel to that of the antero-aboral process. The basal cavity is extended along it
on the aboral side.

M" BRITISH AVONIAN CONODONT FAUNAS

Ligonodina ? sp.
Plate 26, figs. I2a-b

Material, i specimen : figured, X 219.

Range. North Crop 3D 10.

Description. This single specimen is presumably a pathological form of the
genus Ligonodina. It is characterized by the presence of the antero-aboral process
and by the fact that the main denticle can just be discerned when the lighting is
favourable. On the posterior edge of this denticle, however, and continuous with it,
there is a sheet-like development of conodont material which extends in the same
plane as the posterior bar. Only the anterior denticle is visible within this by
reflected light. The denticles of the antero-aboral process are sub-circular in form,
3 in number, and discrete, the middle one of the three being the largest. The form
of the outer lateral face of the extension of the anterior denticle suggests that the
conodont was attached by this surface ; this then became an aboral surface although
in " normal " specimens it would have represented an upper lateral surface.

Genus LONCHODINA Ulrich & Bassler 1926

assler : 219 (nom. nud.).
lrich & Bassler :

Type species. Lonchodina typicalis Ulrich & Bassler 1926.

1925 Lonchodina Bassler : 219 (nom. nud

1926 Lonchodina Ulrich & Bassler :

Lonchodina bolbosa Collinson & Druce

Plate 24, figs. I2a-i4b

1957 Lonchodina nitela Huddle ; Ziegler in Fliigel & Ziegler : 44, PI. 4, fig. 19.
1961 Lonchodina cf. projecta (Ulrich & Bassler) Higgins ; 220, PI. XI, fig. 10.
Lonchodina bolbosa Collinson & Druce (in press).

Material. 12 specimens : figured, X 223, X 222, X 224.
Range. North Crop 3D 8-3D 14/15.

Description. The distinctive features of this species are the relatively sub-equal
short and rather slender bars, the conspicuous basal flaring below the apical denticle
on the outer lateral face and the divergence of the two bars below the denticle at an
angle of more than 90 ° ; in some specimens the angle approaches a right angle, but
in others, the angle may be as high as no°.

The present specimens are very fragmentary but they show the long recurved,
laterally compressed apical denticle, the distinctive flaring cavity, and the straight
and relatively short anterior aboral process described by Collinson & Druce. The
basal excavation below the main denticle is large but shallow, and is extended as a
very narrow groove along the anterior aboral process.

BRITISH AVONIAN CONODONT FAUNAS

141

Lonchodina furnishi Rexroad
Plate 24, figs. 2oa-23C

1957 ? Lonchodina subsymmetrica Ulrich & Bassler ; Bischoff : PI. 1, figs. 19, 21, 22.

1958 Lonchodina furnishi Rexroad : 22, PI. 4, figs. 11-13.
1961 Lonchodina furnishi Rexroad

non 1962 Lonchodina furnishi ? Rexroad
1963 Lonchodina furnishi Rexroad
Lonchodina furnishi Rexroad

Higgins : PI. n, fig. 3.
Higgins : PI. 1, fig. 4.
Bouckaert & Higgins : 17, fig.
Collinson & Druce (in press).

Material. 5 specimens : figured, X 225, X 226, X 228, X 227.

Range. North Crop 3D 8-3D 19.

Description. The distinctive feature of this species is the more or less sym-
metrical development of the cavity below the apical denticle on both sides of the bar,
rather than being restricted to only one side of it. The anterior bar is stout and deep
increasing slightly in depth towards the anterior end. It bears about 5 stout
denticles which are basally confluent but discrete for two thirds of their length.
They tend to be sub-triangular in profile and to be sharply pointed, with sharp
anterior and posterior edges and gently to strongly convex lateral faces. The
curvature on the outer faces tends to be stronger than that on the inner, the denticles
on the median third of the bar tending to be the largest. The anterior denticle is
small and relatively inconspicuous. The apical denticle is about twice the length of
the largest denticle of the anterior bar ; it is strongly posteriorly inclined rather than
recurved, its edges being straight. It lies in approximately the same horizontal plane
as the distal end of the anterior bar. Its inner lateral face is strongly convex at the
base, becoming feebly convex in its upper surface ; its outer lateral face is rather
more strongly convex. Throughout its length it is sharply pointed and is also
directed inwardly as well as posteriorly. The outer lateral face of the anterior bar is
feebly ridged longitudinally along its upper surface, about one third of its depth below
the junction with the oral denticles ; below this point it slopes gently inwards and
has a flat feebly concave surface. The bar itself is curved in a vertical plane and is
also slightly deflected inwardly.

Posterior

Posterior
bar

Apical denticle

Aborai margin

Anted op

Anterior bor

Inner lateral face

Flared basal
cavity

Fig. 28. Lonchodina sp. showing morphological terms used in the text.

i 4 2 BRITISH AVONIAN CONODONT FAUNAS

The posterior bar is depressed, but is more or less straight ; it bears about 4
denticles which are discrete, sub-triangular in profile and sharply pointed, their bases
being confluent ; they have sharp posterior and anterior edges, feebly convex lateral
faces, and are inclined parallel to the apical denticle, though they are not recurved
inwardly to the same extent. The posterior bar is more shallow and slender than
any part of the anterior bar and is only about one third to a half the length of the
latter.

Both bars are excavated by fine longitudinal grooves and there is a conspicuous
flaring cavity below the apical denticle on both the inner and outer lateral faces of the
unit, about which it is sub-symmetrical, though not symmetrical in detail, the inner
lateral flaring occurring rather posterior to the outer lateral flaring.

Remarks. The denticles on the anterior bar may number up to 8 in some
specimens. The species shows some variation in the degree of lateral deflection of
the bars in a horizontal plane. Some specimens (e.g. PI. 24, fig. 23b) show the
posterior bar considerably flexed outward as well as vertically.

Lonchodina obtunda Collinson & Druce
Plate 24, figs. 7a-c

1957 Lonchodina projecta (Ulrich & Bassler) Ziegler in Fliigel & Ziegler : 44, PI. 4, fig. 14

(non PI. 5, fig. 12).
1962 ? Lonchodina cf. projecta (Ulrich & Bassler) Higgins : PI. 1, fig. 5.

Lonchodina obtunda Collinson & Druce (in press).

Material. 5 specimens : figured, X 229.
Range. North Crop 3D 8-3D 17.

Description. The distinctive features of the species are the relatively delicate
construction of the whole unit, the large sub-apical cavity which is developed on the
inner lateral surface, and the very wide angle of divergence of the anterior and
posterior bars, which in Collinson & Druce's type specimens is no "-135 °.

The present specimens are incomplete but they show a relatively slender anterior
bar, with about 5 widely spaced though virtually basally confluent, denticles ; they
are curved upward and inward and have biconvex lateral faces, the inner being the
stronger, and relatively sharp edges. The denticles of the anterior bar range up to
at least 5 in number. The apical denticle is strong and more or less sub-circular in
cross-section, though it has prominent anterior and posterior edges in its proximal
portions ; it is curved inwards and backwards, and its inner lateral face is very
strongly expanded to give a wide flaring basal cavity which extends as a groove along
the bars. The posterior bar is broken in the present specimens but it makes an angle
of considerably more than 90 ° with the anterior bar.

Remarks. Collinson & Druce (in press) have discussed the relationships of
this species with other lonchodinids.

BRITISH AVONIAN CONODONT FAUNAS 143

Lonchodina paraclarki Hass
Plate 24, figs. 16a, b

1953 Lonchodina paraclarki Hass : 83, PL 16, figs. 15, 16.
non 1958 Lonchodina paraclarki Hass ; Stanley : 468, PI. 67, fig. 1.
non 1958 Lonchodina cf. paraclarki Hass ; Rexroad : 22, PL 4, figs. 4, 5.
Lonchodina paraclarki Hass ; Collinson & Druce (in press) .

Material. 3 specimens : figured, X 231.

Range. North Crop 3D 10-3D 14/15.

Description. The most distinctive features are the very short posterior bar
tending to develop only 2 denticles, the massive incurved and recurved apical
denticle, and the very strong inner-lateral deflection of its aboral margin, giving a
sub-triangular basal cavity that extends along most of the aboral surface of the unit.
Hass has discussed the relationship of the species to Ligonodina clarki (1953 : 83)
and Collinson & Druce have discussed the differences between Lonchodina paraclarki
in the original sense of Hass and specimens referred to that species by Stanley &
Rexroad.

Lonchodina paraclaviger Rexroad
Plate 24, figs. 15a, b, 18a, b

1958 Lonchodina paraclaviger Rexroad : 22, PL 4, figs. 7-10.

Lonchodina paraclaviger Rexroad ; Collinson & Druce (in press) .

Material. 780 specimens : figured X 232, X 233.

Range. North Crop 3D 13-3D 14/15.

Description. This species is characterized by its stout general construction.
The posterior bar is about half the length of the anterior bar. The stout, basally
confluent, elongated, pointed denticles, number eight on the anterior bar, and four on
the posterior. Both bars are straight except for slight curvature in the anterior,
where they make an angle of about 90°-ioo° with each other. The lateral deflection
of the posterior bar is about 45 ° out of the vertical plane of the anterior bar, and a
large flaring asymmetrical cavity is strongly developed on the inner side, as a sub-
triangular, to rounded expansion, that is flat on the outer lateral face and is extended
along both bars as a deep groove. Both bars are relatively deep, with convex lateral
faces. The denticles of the anterior bar, although basally confluent, are discrete for
most of their length, and approach the apical denticle in size ; they may be of
uniform size or they may increase in size towards the anterior end of the unit ; they
are slightly recurved posteriorly and also inwardly, and lie more or less parallel to the
apical denticle, which is sometimes only slightly larger than those of the anterior bar.
The apical denticle is very strongly convex on its inner lateral face, with sharp
anterior and posterior edges, and rather less strongly convex on its outer lateral face ;
it is more or less straight in lateral view but is inclined posteriorly at about 60 ° to the
anterior bar and is also recurved inwardly. The denticles of the posterior bar tend

i 4 4 BRITISH AVONIAN CONODONT FAUNAS

to be rather straight, but are discrete, sharply pointed, and tend to be directed
inwardly, being either erect to the posterior bar or in a few cases sloping slightly
forward ; in most specimens, however, they are either erect or posteriorly inclined.
The posterior denticles tend to decrease in size posteriorly.

The basal cavity is strongly developed on the inner side of the unit, but it is wide,
rather than deep ; it extends as a very narrow groove along the bars.

Lonchodina transitans Collinson & Druce
Plate 31, fig. 14
Lonchodina transitans Collinson & Druce (in press).

Material. 3 specimens : figured, X 234.

Range. North Crop 3D 4-3D 14/15.

Description. The present specimens are incomplete but they show the essential
features of the species, including the angle of divergence of the anterior and posterior
bars of about 130 ° and the more or less bilaterally asymmetrical open " ligonodina "
type cavity which is developed below the apical denticle. The apical denticle is
recurved and relatively slender. The posterior bar is broken in the present speci-
mens but bears at least 2 discrete, sharply pointed, posteriorly inclined denticles. The
anterior bar is straight, and is slightly inflexed, as well as being depressed ; it bears
at least 3 laterally compressed, recurved, slightly incurved denticles. Both bars are
excavated by aboral grooves which extend into the shallow and rather flared cavity
below the basal surface of the apical denticle. The apical denticle is biconvex in
cross-section in its proximal part, and its strong lateral expansion on the outer face
develops a suggestion of a median ridge on the lower part of that surface.

Remarks. Collinson & Druce have pointed out that this species represents a
transitional form between the genera Ligonodina and Lonchodina.

Lonchodina sp. A
Plate 24, figs. 17a, b

Material. 6 specimens : figured, X 424.

Range. North Crop ZLA 32-ZLA 33.

Description. All the present specimens are broken, but they appear to represent
a short unit, the bars being restricted. The apical denticle is large, laterally com-
pressed and inclined toward the inner side. The bars appear to be curved on the
outer side. The basal cavity is large and occurs beneath the apical denticle.

Genus MAGNILATERELLA Rexroad & Collinson 1963
1963 Magnilaterella Rexroad & Collinson : n.
Type species. Magnilaterella robusta Rexroad & Collinson 1963.

BRITISH AVONIAN CONODONT FAUNAS 145

Magnilaterella complect ens (Clarke)
Plate 23, figs. I4a-i7c

1900 Prioniodus tulensis Hinde (partim) : 343, PI. 9, fig. 16.

1928 Prioniodus tulensis Hinde ; Holmes (partim) : 22, PI. 3, fig. 20.

i960 Ligonodina complectens Clarke : 9, PI. 1, figs. 14, 15.

Material. 14 specimens : figured, X 240, X 237, X 238, X 239.
Range. Scotland HOSIE 2A-HOSIE 2B.

Description. This species is clearly a member of the genus Magnilaterella
Rexroad & Collinson, but is not typical of that genus. The generic features are seen
in the present specimens in the short form, strong inner lateral callus and basal
groove of the lateral bar, and the deflected and upflexed general form of the posterior
bar, the largest denticles of which are situated at the proximal end and which are
strongly developed and strongly recurved and incurved. In contrast to other
described forms of the genus Magnilaterella, however, the largest denticles of the
lateral bar are situated at the anterior, and not at the posterior end. This form,
therefore, seems to approach Ligonodina, to which Magnilaterella is closely related.
Rexroad & Collinson (1963 : 13) have discussed the relationships between the two
genera, but the character of the present specimen alters the view of the distinctive
nature of the denticulation of the posterior bar.

The lateral bar is short and in inner view is deep ; the most anterior denticle is
enormously developed and strongly recurved in its lower portion, its distal half being
more or less straight, although the distal posterior edge is so sharply pointed that it
gives it almost a sigmoidal appearance. The two remaining denticles of the posterior
bar are inconspicuous by comparison with the major denticle ; they are isolated,
small, sub-circular, and more or less sharply pointed. The posterior bar is curved
sharply backward and upward and the proximal denticle is very strongly developed.
It approaches, but does not quite equal, the major denticle in size ; it is biconvex in
cross-section, with bluntly developed anterior and posterior ridges in its upper half,
but in the proximal half it is convex on the anterior face and has a concave posterior
depression on its posterior edge. The inner lateral face is strongly convex and it
bears at least one small isolated sub-circular denticle. The largest denticle of the
posterior bar is recurved and deflected parallel to the major denticle.

The aboral surface of the unit is conspicuously grooved ; the outer aboral surface
tends to be flat and rather extended below the major denticle, but the inner aboral
surface is strongly developed as a callus, which runs up the inner face of the lateral
bar. This slopes down to give a relatively narrow, horizontal, aboral surface,
parallel to the base of the groove. In more complete specimens the lateral bar is seen
to taper to a point at its distal end ; it may bear only 2 denticles including the most
anterior denticle. In more complete specimens the posterior bar may bear up to 6
denticles in specimens which tend to decrease distally in size ; when viewed orally it
makes an angle of about 30 ° with the lateral bar. In the specimen shown in PI. 23,
fig. 14 a small and relatively inconspicuous denticle is developed in front of the largest

146 BRITISH AVONIAN CONODONT FAUNAS

denticle of the lateral bar, being about equal in height to the larger denticles of the
posterior bar.

When viewed aborally the most striking feature of this species is the broad
extension of the aboral surface, represented by the flange, and the restriction of the
warped and flexed sinuous cavity to the outer lateral margin of the scar, which the
flange forms.

Magnilaterella clarkei sp. nov.
Plate 23, figs. n-i3b

1900 Polygnathus convexus Hinde [partim) : 342, PI. 9, fig. 7.

1928 Lonchodus convexus (Hinde) Holmes (partim) : 14, PI. 6, fig. 14.

i960 " Gen. et sp. nov? " Clarke : 16, PI. 11, figs. 10, 12, 13.

Derivation of name. After Dr. W. J. Clarke.

Diagnosis. Magnilaterella characterized by massive development of strongly
depressed, continuously curved posterior bar, gently flexed inward in its median part,
its denticles tending to be largest in its mid-third. Denticles of lateral bar large,
sub-triangular, separated by smaller single denticles. Posterior bar of insignificant
size in comparison with lateral bar, but strongly inflexed.

Material. 23 specimens : Holotype X 431, Paratypes X 241, X 432 (all
figured).

Range. Scotland DUN 52-80, GILM 3-BIL 102.

Description. This is a rather typical species of the genus Magnilaterella, with a
very elongated and very deep posterior bar, which becomes deeper in its posterior
part. It has a very feebly convex inner-lateral face and is bowed slightly out-
wards along its length. It is continually recurved with a conspicuous concave aboral
surface. The oral surface bears up to 4 main denticles, which tend to be largest in
the median third and decrease in size in both directions. They are conspicuously
triangular in lateral view and are sharply pointed. The denticles have very sharp

inner lateral face

Lateral bar

Basol groove
Fig. 29. Magnilaterella sp. showing morphological terms used in the text.

BRITISH AVONIAN CONODONT FAUNAS 147

anterior and posterior edges and feebly convex to flat lateral faces. They are
separated by a single similar denticle, widely spaced between them but only about
one fifth to one sixth of the length of the larger denticles they separate. The
posterior end of the lateral bar is marked by one such denticle which extends
downwards to form the bluntly triangular distal end of the bar. At the anterior end
of the lateral bar there are 2 to 3 smaller denticles of this general kind. The inner
aboral surface of the posterior bar is marked by a variably developed flange, which
although laterally persistent is irregular in the extent to which it invades the lateral
face of the unit. It tends to do this to a rather small degree and its greatest aboral
extension is under the posterior third of the bar.

The posterior bar is very small in comparison with the lateral bar and is strongly
recurved, so that in oral view it makes an angle of about 30 ° with the lateral bar. It
is also sharply convex and seems to bear rather small denticles although in the present
specimens it is broken. The largest of these small denticles, occurs at its junction
with the lateral bar. It tends to decrease in depth distally at its junction with the
lateral bar, just anterior to the bluntly spatulate termination of the latter. In outer
lateral view the outer lateral bar is flat and the outer lateral surface of the denticles
are also markedly flat ; only a few of them show any degree of convexity. There is no
sign in outer lateral view of the scar-like presence of the inner callus. In aboral view
a thin slit occurs along the length of the lateral blade and is also developed, though in
much reduced width, below the posterior bar.

Remarks. The specimens referred to this species show some variation in the
development of the callus on the inner lateral face and also in the depth of the lateral
bar, which tends in some specimens to be deeper in its medial third than its distal
third.

Magnilaterella contraria sp. nov.
Plate 23, figs. 8a-c, i8a-c

1941 Ligonodina ? sp. Branson & Mehl : 171, PI. 5, fig. 11.
1963 New Gen. et sp. Rexroad & Collinson : 21, PI. 3, fig. 2.

Derivation of name. With reference to the morphology.

Diagnosis. Magnilaterella characterized by very delicate and slender construc-
tion. Short lateral bar bearing three isolated and recurved denticles, the largest
being the middle : bar very shallow decreasing in height posteriorly, and making an
obtuse angle with posterior bar.

Material. 3 specimens : Holotype X 553, Paratype X 517 (both figured).

Type locality and horizon. North Crop. Sample 3D 23.

Range. North Crop 3D 23.

Description. The lateral bar is short and more or less straight in a vertical plane
but is strongly recurved, so that its basal surface is continuously concave in lateral
view. It is of very slender construction and bears only 3 or 4 denticles, the two in
the medial part being much larger than those at either end. The denticles are

148 BRITISH AVONIAN CONODONT FAUNAS

recurved, but their axes are straight and sharply pointed ; they have sharp anterior
and posterior edges and strongly convex lateral faces, their proximal portions tending
to become flatter towards their apices ; they are about four to five times as long as
the other denticles on the unit. The inner lateral face of the lateral bar is marked by
a callus, which is not conspicuous and does not extend far up the lateral face : the
bar decreases in width posteriorly and its posterior end is marked by a very small
denticle, the posterior aboral margin being bluntly rounded ; the bar may be very
slightly flexed outward in a vertical plane, but it is essentially straight.

The posterior bar is of unknown length ; it bears at least one small denticle near its
junction with the lateral bar. It is excavated by a narrow groove which extends
continuously below the lateral bar.

Remarks. Rexroad & Collinson (1963 : 21), described forms closely similar to
this species, but did not include them in the genus Magnilaterella. They did not
state the reasons for this exclusion, but these presumably involve the relatively
slight difference in the form of the basal cavity, which in the present specimens tends
to be medial rather than lateral on the two bars, the restricted nature of the callus,
and the fact that the posterior denticle of the lateral bar is not the largest of those
developed.

Other specimens described above in the present paper show that none of these
characteristics is wholly distinctive of the genus Magnilaterella. Some species
which are, on all other morphological criteria, " good " species of the genus, do not
have the posterior denticle more strongly developed than the rest of the series, and
the form of the callus is a highly variable feature ; it, therefore, seems to us that there
is no good reason for excluding this species from the genus.

Magnilaterella robusta Rexroad & Collinson
Plate 31, figs. 25, 26, 27

1941 Lonchodina sp. Branson & Mehl (partim) : 171, PI. 5, fig. 10 only.

1956 Metalonchodina ? sp. Elias : 124, PI. 5, fig. 3.

1957 Genus Indeterminate Rexroad (partim) : 42, PI. 4, figs. 19-21 only.

1958 Genus Indeterminate Rexroad : 26, PI. 5, figs. 1, 2.

1963 Magnilaterella robusta Rexroad & Collinson : 14, PI. 2, figs. 4, 5, 9, text-figs. 3, 4.

1964 Magnilaterella robusta Rexroad & Collinson ; Rexroad & Furnish : 673, PI. 111, figs.

27-3I-

1965 Magnilaterella robusta Rexroad & Collinson ; Rexroad & Nicoll : 22, 23, PI. 1, figs.

10, n.

Material. 3 specimens : figured, X 528, X 529, X 548.

Range. Scotland Samples DUN 78-79.

Description. Well preserved specimens from our Scottish faunas are very
closely similar to those illustrated and described by Rexroad and Collinson. The
inner lateral process is short and stout, and is strongly recurved and very strongly
arched. It bears up to 6 denticles, those near the apex being the largest. The
posterior bar is small and relatively straight. It is strongly flexed and bears only
1 or 2 denticles, that nearest the anterior end being the largest.

BRITISH AVONIAN CONODONT FAUNAS 149

Magnilaterella sp.

Plate 23, fig. 9

Material, i specimen : figured, X 244.

Range. Scotland GILM 2.

Description. A single specimen of doubtful affinities is referred to this genus.
It is characterized by the distinctive callus developed on the inner face of the lateral
bar and the slit-like excavation developed on both bars. The posterior bar is very
short and may not be broken. The lateral bar bears two denticles which are discrete,
inclined and sharply pointed ; the bar is broken and is of unknown length. The
posterior bar bears a single denticle at its junction with the lateral bar ; the denticle
is short but sharply pointed, being only about one sixth to one seventh the length of
the posterior bar.

Magnilaterella spp.
Plate 23, fig. 10 ; Plate 31, figs. 5, n

Material. 649 specimens : figured, X 242, X 322, X 323.
Range. Avon Gorge Z 35-C 24, North Crop CYD 6-3D 17.

Description. Fragmentary specimens of Magnilaterella are relatively common
in the upper part of the D Zone and elsewhere. Few of them are sufficiently com-
plete to enable specific identification, but some of them probably represent new
species. We illustrate three extreme forms.

Plate 31, fig. 11 (X 322) shows a form with characteristically deep and strong
posterior bar, the inner lateral face of which bears a well-developed callus and basal
groove, which is thin but conspicuous and long. The apical denticle is very strongly
developed, and has four to five times the basal width of other denticles of the posterior
bar. The lateral bar is very strongly flexed, and the denticles decrease rapidly in
size towards the distal end.

Plate 31, fig. 5 (X 323) shows a form characterized by much more slender construc-
tion. The apical denticle is elongated and gently curved posteriorly and inwards.
It is sharply pointed and its general construction is slender. The callus is con-
spicuous, but shallow, and the lateral bar, which lies at about 90 ° in both a horizontal
and vertical plane to that of the posterior bar, has its main flexure at its junction with
the posterior bar rather than being continuously recurved.

Magnilaterella ? sp.
Plate 23, figs. 7a, b

Material, i specimen : figured, X 447.

Range. North Crop ZLA 37.

Description. This specimen consists of an antero-lateral and a posterior bar.
The major denticle is smaller than the denticles on the posterior bar and lies in

150 BRITISH AVONIAN CONODONT FAUNAS

between the planes of the two bars. The anterior bar is lateral and deflected, bearing
3 isolated denticles. The posterior bar bears 3 large, posteriorly inclined denticles.

Genus MESTOGNATHUS Bischoff 1957
1957 Mestognathus Bischoff : 36.

Type species. Mestognathus beckmanni Bischoff 1957.

Diagnosis. A canoe-shaped form, with a well-developed platform, tapering to
anterior and posterior. The platform ornamented by numerous transverse ridges.
A high anterior blade developed on the outer side of the platform ; inner side of the
platform, in lateral view, extends further to the anterior, than the outer side of the
platform, because of the development of the anterior blade on the latter. A deep
trough runs along mid-length of oral surface. Aborally a small narrow basal cavity
present.

Remarks. The genus Mestognathus Bischoff closely resembles Cavusgnathus
Harris & Hollingsworth, but differs from the latter genus in that it has a small
narrow basal cavity compared with the wide flaring basal cavity typical of Cavus-
gnathus. Mestognathus has not been recorded from North America and makes its
first appearance in Europe in Cu II (3/y. In North America Cavusgnathus makes its
first appearance at nearly the same horizon and so the two genera may be closely
related.

Mestognathus beckmanni Bischoff
Plate 15, figs. 7a-d

1957 Mestognathus beckmanni Bischoff : 37, PI. 2, figs. 4a, b, c, d, 5, 6, 8, 9.

i960 Mestognathus beckmanni Bischoff ; Kronberg, Pilger, Scherp & Ziegler : 14, PL 3,

figs, ia, b.
1962 Mestognathus beckmanni Bischoff ; Meischner : text-fig. 10.
1962 Mestognathus beckmanni Bischoff ; Bartenstein & Bischoff : Tab. 3.

Material. 36 specimens : figured, X 245.

Range. North Crop CYD 7, Avon Gorge C 15-D 26.

Description. The carina is restricted to the posterior part of the platform in this
species, but may in some cases be extended anteriorly to meet the inner lateral face
at a narrow angle. The anterior blade is high and has from 6 to 12 denticles which
occupy the anterior margin of the outer side of the platform. The medial trough is
deep and very wide, and runs for at least half the length of the platform, being
deepest anteriorly. The unit is about four times as long as it is wide, being widest
at about mid-length of the platform. In outer lateral view the highest part of the
anterior blade is about twice the depth of the posterior platform at mid-point. The
anterior blade is characterized in lateral view by the development of from 6 to 12
denticles which are basally fused, only their tips being discrete. They tend to be of
variable size and to have bluntly rounded apices with gently convex lateral faces.
The largest denticles are the posterior one or two on the blade, especially the most

BRITISH AVONIAN CONODONT FAUNAS 151

posterior. This tends to be sub-triangular in form, and is inclined posteriorly, with
strongly convex lateral faces and blunt anterior and posterior edges. Its inner
lateral face is flatter than its outer. The other denticles stand more or less erect to
the bar but their inclination is rather variable. The anterior blade is inclined gently
inwards ; there is a tendency for the denticles, to show some reduction in height
anteriorly and the anterior blade projects beyond the platform at the anterior end.
In oral view a deep trough is developed parallel to the anterior blade, being widest
and deepest anteriorly. It shallows towards the position of maximum width of the
posterior platform and becomes obsolescent in the posterior half. It is broadly U-
shaped. The outer margins of the carina are decorated with feeble to moderate
transverse ornament, which tends to be aligned acutely to the length of the unit,
forming an arrow-type structure pointing forward, rather than being developed at
right angles. There are about 12 of these ridges on the outer side of the platform
and about 17 on the inner. They become rapidly obsolescent towards the middle of
the platform and are more feebly developed on the inner than on the outer side.
There is a variable posterior carina developed in the posterior part of the unit,
consisting of a low ridge of only barely distinguishable nodose denticles, but it may be
extended anteriorly to meet the antero-lateral inner edge of the platform as a low
inconspicuous ridge, dividing the platform into two unequal parts. It runs to the
left of the medial trough. The outline of the platform in oral view is such that the
anterior two-thirds of the inner lateral margin is straight and the posterior third
inclined towards its pointed posterior termination. The outer lateral face is straight
in its anterior half and gently concave in its posterior half, the whole appearance of
the unit being pinched towards the posterior fifth. The anterior inner lateral edge
terminates in an undenticulate projection. The edges of the platform are feebly up-
turned. In inner lateral view the antero-inner face of the platform is flat, with sharp
oral and aboral lateral edges. The lateral face decreases in width towards the mid-
point, beyond which the platform has a thin lateral face which merges with the base.
The outer lateral face is characterized by having a flat surface, parallel to the
denticles, with a longitudinal ridge developed about the base of them, and then a
sloping lateral face which slopes towards the basal cavity below the ridge. In outer
lateral view the posterior half has a lateral face, which slopes steadily towards the
basal cavity.

Anterior blade Outerslde of platform

Platform

Carina Posterior

Inner lateral face

v Trough

Fig. 30. Mestognathus sp. showing morphological terms used in the text.

152 BRITISH AVONIAN CONODONT FAUNAS

The basal surface is characterized by a restricted median cavity, which is shallow
and occupies the anterior half of the platform. It extends anteriorly and posteriorly
as a very narrow shallow slit along the unit.

Mestognathus bipluti Higgins

Plate 25, figs. ia-3c, 8a, b

1961 Mestognathus bipluti Higgins : 216, PI. 10, figs. 1, 2 ; text-fig. 4.

Diagnosis. This species is characterized by a short, deep blade which diverges at
the anterior end of the unit from the antero-inner lateral edge of the platform.
Slender and pointed platform has a more or less prominent median carina.

Material. 3 specimens : figured, X 249, X 248, X 246, X 247.

Range. North Crop CYD 6-CYD 7.

Description. This species of conodont has an outline that is reminiscent to some
extent of a folsom-point. The inner edge of the platform is straight in the anterior
two thirds and then turns rapidly inwards towards the pointed posterior end. The
posterior third is also straight and the bend is sharply angular. The outer lateral
margin of the platform is straight in its anterior third and up to the end of the
anterior blade, but posteriorly it is turned sharply inwards towards the pointed
posterior end. The posterior outer lateral face is more or less straight. There is a
strongly developed posterior carina, which consists of a series of confluent nodes, and
extends about half the length of the platform. It is continued less obviously
anteriorly to meet the antero-inner lateral point as a low inconspicuous ridge. There
is a narrow deep trough adjacent to the blade and this becomes shallower and
obsolescent posteriorly, extending on the outer side of the median carina. The inner
lateral portion of the platform adjacent to the carina tends to be flat or feebly con-
cave. The margins of the platform are ornamented by relatively strongly developed
transverse ridges, which tend to become less conspicuous towards the posterior end.
They extend about half the distance from the lateral margins to the carina. The
lateral margins themselves are gently up-flexed. The downward and outward
curvature of the antero-aboral portion of the blade is a conspicuous feature in oral
view, as is the divergence of the anterior blade and the antero-inner edge of the
platform to give a branched structure.

In aboral view this latter feature is the most conspicuous characteristic of the
species. The total length of the branches are a third to a quarter of the length of the
platform. The medial cavity is very small and inconspicuous and is only slightly
flared. It extends anteriorly and posteriorly as a keeled narrow slit along the
median line of the unit. The main cavity is situated near the junction of the blade.

In inner lateral view the oral surface of the unit is bluntly serrated and the posterior
end is bluntly spatulate. In outer lateral view the aboral margin is straight in
the posterior half, but gently concave in the anterior half. In outer lateral view
the anterior blade is a very distinctive feature. The posterior denticle is the largest
and the blade decreases regularly in depth towards the bluntly spatulate anterior end.

BRITISH AVONIAN CONODONT FAUNAS 153

The denticles form a fused series of bluntly pointed confluent denticles, about 5 or
6 in number, grading in the antero-aboral region into minute and inconspicuous
confluent denticles. The antero-aboral portion is flexed sharply outwards ; the
posterior denticle is inclined slightly posteriorly. The whole posterior outer lateral
face of the platform slopes gently inwards to meet the basal slit, giving a boat-like
appearance to the unit in lateral view. It is convex to flat in its upper part and may
become concave in its postero-aboral portion. In inner lateral view the same feature
is seen. The platform is relatively straight in its posterior third, but is regularly
concave in its anterior third or half. The inner lateral margin is generally developed
at a lower level than the outer lateral margin, and is finely denticulated, the inner
anterior edge of the platform bearing rather conspicuous low denticles. The antero-
aboral inner edge is strongly convex and is deflected inwards. It is much less deep
than the corresponding outer aboral anterior edge.

Mestognathus neddensis sp.

Plate 15, figs. 4a-6c

nov.

Derivation of name. From the River Nedd, Breconshire.

Diagnosis. Mestognathid with short deep anterior blade, bearing 6 denticles,
those at anterior end being only slightly shorter than those at posterior ; their apices
are discrete. Anterior blade and inner anterior edge of platform bifurcate at the
anterior end of the unit. Posterior platform straight on outer lateral side and gently
convex on inner lateral side, posterior inner lateral portion being strongly pinched
inwards towards pointed posterior end. Strong posterior carina, consisting of low
rounded nodes along posterior half of platform, becoming obsolescent towards
anterior inner lateral edge of platform.

Material. 5 specimens : Holotype X 250, Paratypes X 251, X 252 (all figured).

Type locality and horizon. North Crop. Sample CYD 6.

Range. North Crop CYD 6-CYD 7.

Description. In oral view the unit is elongated and slender. The anterior blade
is free for only a very small portion of its length, but the anterior end of the platform
is marked by a V-shaped indentation, formed by the junction of the anterior blade
and the inner anterior margin of the platform. The blade is conspicuously denticu-
lated in oral view and the outer lateral margin of the platform is more or less straight.
It is ornamented by a series of transverse denticles which are more strongly developed
in the anterior portion than "the posterior. The inner lateral platform is gently
sinuous, being straight to gently concave in the anterior third and strongly convex in
the posterior two thirds. The posterior carina extends beyond the posterior limit
of the platform, so the whole appearance of the platform is rather pinched posteriorly.
The inner lateral margin of the platform is ornamented by feeble, nodular to trans-
verse ridges which become obsolescent towards the anterior part. The posterior
half of the platform is marked by a conspicuous carina, consisting of 7 or 8 low
rounded fused nodes, and is extended as a rather inconspicuous ridge towards the

154 BRITISH AVONIAN CONODONT FAUNAS

anterior inner lateral edge of the unit. There is a narrow V-shaped trough developed
adjacent to the blade, running towards the posterior end of the unit on the outer
margin of the carina, and becoming shallower and narrower posteriorly. In outer
lateral view the blade is conspicuously deeper than the platform. It is of regular
depth throughout its length and in some specimens shows a tendency to increase
anteriorly in depth. It is very bluntly rounded antero-aborally, and is strongly
down-flexed in relation to the blade. Although the junction between the two is
curved, the anterior aboral edge of the blade makes an angle of about 45 ° with the
aboral edge of the posterior platform. The oral surface of the blade bears 6 or 7
fused denticles, the apical tips of which are discrete and bluntly rounded.

In outer lateral view the posterior platform has a bluntly serrated surface and its
outer lateral face slopes down sharply towards the median aboral keel. The
posterior end is more or less flat, and the denticles of the posterior median carina tend
to be higher in outer lateral view than those on the edge of the platform. The
posterior third of the platform is straight, but the anterior part is gently concave.
The denticles of the anterior blade are more or less uniform in height, although the
most posterior tends in some specimens to be rather larger than the rest. They are
more or less erect, though the most posterior denticle may be slightly inclined
posteriorly.

In inner lateral view the aboral surface of the whole unit appears to be gently
convex, except for the rather straight posterior termination. The oral edge is more
or less conspicuously serrated by low nodose confluent nodes, and the anterior inner
edge is frequently developed into one or two rather conspicuous denticles, its antero-
aboral margin being bluntly pointed and making a very prominent bifid junction with
the anterior blade. The extension of the posterior carina is a prominent feature in
this inner lateral view. The inner oral margin of the platform is strongly convex,
but it flattens off along the mid-height of the unit, and the lower part is flat to
strongly concave, sloping rapidly towards the elongated aboral keel.

In aboral view there is a prominent, but very small, median pit with inconspicuous
edges, which is developed near the junction of the blade of the platform. It is
biconvex in outline and is elongated antero-posteriorly. A shallow rather flat aboral
surface extends posteriorly from it along the unit with an inconspicuous median slit
developed towards the posterior end. Anteriorly a thin slit runs towards the
junction of the inner anterior edge with the anterior blade.

The posterior end of the platform is marked by a more or less vertical face, with
rounded posterior aboral margin. The platform deepens towards the anterior inner
edge when seen in inner lateral view, and this is a conspicuous feature of the unit.

Genus METALONCHODINA Branson & Mehl 1941
Type species. Prioniodus bidentatus Gunnell 193 1.

Metalonchodina bidentata (Gunnell)
Plate 24, figs. 8a-nb
1900 Polygnathus convexus Hinde (partim) : 342, PI. 9, fig. 8.

BRITISH AVONIAN CONODONT FAUNAS 155

1928 Lonchodus convexus (Hinde) Holmes (partim) : 14, PI. 6, fig. 13.

1931 Prioniodus bidentatus Gunnell 247, PL 29, fig. 6.

1933 Prioniodus dactylodus Gunnell 265, PI. 31, fig. 1.

1941 Metalonchodina bidentata (Gunnell) Branson & Mehl : 106, PI. 19, fig. 34.

1941 Metalognathus bidentata (Gunnell) Ellison : 116, PI. 20, figs. 35, 36.

1952 Metalognathus bidentata (Gunnell) Rhodes : 898, PI. 128 ' m '.

1957 Metalonchodina bidentata (Gunnell) Bischoff : 37, PI. 5, figs. 13, 15, 46.

i960 Metalonchodina conflecta Clarke : 17, PI. 2, fig. 14.

1961 Metalonchodina bidentata (Branson & Mehl) Higgins : PI. 12, fig. 9.

1962 Metalonchodina bidentata (Gunnell) Higgins : PI. 1, fig. 3.
1964 Lonchodina ? nipponica Igo & Koike : 186, PI. 27, fig. 20.

1964 Metalonchodina sp. Rexroad & Furnish : 673, PI. 111, fig. 7.

1965 Metalonchodina fragilis Murray & Chronic : 605, PI. 73, figs. 19, 20.
Metalonchodina bidentata (Gunnell) Collinson & Druce (in press).

Material. 6 specimens : figured, X 253, X 254, X 255, X 256.

Range. North Crop 3D 10-3D 14/15.

Description. The present specimens agree closely with Branson & Mehl's
(1941 : 106) definition of the species. The anterior limb is shorter than the posterior
bar and bears a massive denticle or pair of denticles upon it. In aboral view the
most conspicuous feature is the very strong lateral flexing below the apex of the two
bars. The small and fairly shallow pit is situated in the middle of the strongly
laterally expanded aboral surfaces at this point ; the aboral surfaces of each limb
being relatively flat or obtusely V-shaped. They are excavated by very narrow
shallow slit-like cavities along their lengths. The chief expansion of the base below
the apical denticle is concentrated on the inner lateral side and is a very prominent
feature of the unit. In inner lateral view the most conspicuous feature of the unit is
the enormous size of the denticle developed on the anterior bar. This is about two
to three times as wide as any of the other denticles, has straight anterior and posterior
edges and is bluntly pointed. It has gently convex inner and outer lateral faces.
The anterior edge of the unit is developed into a triangular pointed anterior end. Its
aboral margin is straight, and although its junction with the posterior bar is curved,
it makes an angle of 80 °-o,o ° with the aboral surface of the latter. The posterior bar
bears two or three smaller denticles, sub-circular in cross-section, with inconspicuous
anterior and posterior edges, which are inclined anteriorly.

Apical denticle

-Main denticle

Inner loterol

aboral expansion ./v ""^"\;J ' Anterior limb

Posterior bor V N Aboral margin

Fig. 31. Metalonchodina sp. showing morphological terms used in the text.

156 BRITISH AVONIAN CONODONT FAUNAS

The apical denticle is smaller than the large denticle on the anterior bar but of
similar general form. Its most conspicuous feature is the very strong, internal lateral
extension of the aboral portion, to form the inner lateral flange. On the aboral
margins both the anterior and the posterior bars are more or less straight. Their
most striking feature in inner lateral view is the development of a longitudinal ridge
parallel to their bases, which rises higher on the faces towards the apex, and
represents the bevelled margin of the flattened aboral surface.

In lateral view this latter feature is less conspicuous and the whole unit is flat to
feebly convex in general form.

Remarks. This species shows appreciable variation. The specimens illustrated
in PI. 24, figs. 8, 10 and n are closely similar. That of PI. 24, fig. 9, resembles them
in overall form but has an additional denticle developed anterior to the main denticle
of the anterior bar, and the apical and posterior denticles also tend to be more sub-
circular than those of typical members of the species. Similarly, other specimens
have two smaller denticles developed anterior to the main denticle of the anterior bar
and also have more sub-circular denticles. It may be that these specimens should be
regarded as distinct species but they are provisionally included in Metalonchodina
bidentata.

Genus NEOPRIONIODUS Rhodes & Muller 1956

1956 Neoprioniodus Rhodes & Muller : 698.
Type species. Prioniodus conjunctus Gunnell 1931.

Neoprioniodus antespathatus Collinson & Druce
Plate 21, figs, ioa-nb
Neoprioniodus antespathatus Collinson & Druce (in press).

Material. 2 specimens : figured, X 257, X 258.

Range. North Crop 3D 8-3D 16.

Description. This is a neoprioniodid with a slender anteriorly directed anterior
denticle, with sharp anterior edge, blunt posterior edge, and biconvex outline. The
posterior bar is slender, decreasing in depth posteriorly, and it has a conspicuously
concave junction with the aboral process. Its oral surface bears a series of about 9
denticles, the largest of which are in the anterior half, and which show a broad
tendency to decrease in size posteriorly, though this tendency is not conspicuous or
regular. The denticles are basally confluent, but are discrete for most of their
length. They are of slender general form, with sharp anterior and posterior edges

BRITISH AVONIAN CONODONT FAUNAS

157

and gently convex lateral faces. They stand more or less erect or gently posteriorly
inclined in relation to the underlying aboral surface of the bar. The posterior bar is
gently down-curved, although its distal portion is more or less straight. The aboral
projection of the anterior denticle is the most massive feature of the unit. It is
about twice as wide in lateral view as the basal part of the anterior denticle itself.
Its anterior margin is straight to very gently concave and its anterior aboral termina-
tion is bluntly pointed. Its posterior aboral margin is very strongly convex and it
decreases in width towards its distal end. The whole effect is of a massive structure.
Its lateral faces are more or less flat but the whole unit is feebly curved inwardly.

In outer lateral view the whole unit is convex, reflecting the inward recurvature.
In aboral view there is a very inconspicuous cavity developed below the apical
denticle ; the aboral surfaces of the posterior bar and the aboral process are flat in
general form, the inner lateral aboral edge being slightly higher than the lower, and
the whole surface is excavated by a minutely narrow and shallow longitudinal groove.

The most conspicuous features of this unit are the slender form of the anterior
denticle and the posterior bar, in contrast to the massive form of the aboral process,
the whole anterior lateral aboral face of which is more or less concave.

Anterior denticle

Anterior edge

Aboral
process

Denticles of posterior bar

Posterior

Posterior bar

Aboral edge

Fig. 32. Neoprioniodus sp. showing morphological terms used in the text.

158 BRITISH AVONIAN CONODONT FAUNAS

Neoprioniodus barbatus (Branson & Mehl)
Plate 21, figs. 4-7

1934 Prioniodus barbatus Branson & Mehl : 288, PI. 23, figs. 19, 20.

1934 Prioniodus corniger E. R. Branson : 329, PI. 28, fig. 2.

1938 Prioniodus barbatus Branson & Mehl ; Branson & Mehl : 144, PI. 33, fig. 21, pi. 34,

figs. 28, 32.

1938 Prioniodus corniger (?) E. R. Branson ; Branson & Mehl : 143, PI. 34, fig. 19.

1944 Prioniodus barbatus Branson & Mehl ; E. B. Branson : 221, PI. 39, figs. 28, 32.

1944 Prioniodus corniger (?) E. R. Branson ; E. B. Branson : 221, PI. 39, fig. 19.

1949 Prioniodus barbatus Branson & Mehl ; Thomas : 411, PI. 4, fig. 26.

1949 Prioniodus corniger E. R. Branson ; Thomas : 411, PI. 4, fig. 27.

1956 Prioniodina barbata (Branson & Mehl) Bischoff & Ziegler : 160, PI. 13, figs. 19, 20.

Material. 674 specimens : figured, X 259, X 260, X 261, X 262.
Range. North Crop KL 13-ZL 9, Avon Gorge K 21-C 16.

Description. The anterior denticle is very tall, slender, laterally compressed, and
ovate in cross-section. It is continuously and gently recurved toward the posterior,
terminating in a fine point. The posterior bar is fairly deep, being deepest at the
anterior and shallowing regularly towards the posterior. It bears 9 to 12 tall needle-
like denticles, sub-circular in cross-section, which are fused at their bases but free at
their tips. In the posterior part there is some twisting of the bar and it is down-
curved slightly.

The basal cavity is situated on the aboro-posterior side of the anterior denticle,
which is produced below the posterior bar to form an aboral process. The complete
aboro-posterior surface is excavated, though there is comparatively little flaring of
the lips, and the cavity may run for a short distance beneath the posterior bar. In
most specimens the aboro-posterior outline of the aboral process is gently convex,
but in some specimens a flange tends to develop, making it sigmoidal in outline
(e.g. PI. 21, fig. 6).

Remarks. This appears to be a very common Avonian species, especially in the
middle of the Z Zone.

Neoprioniodus confluens (Branson & Mehl)
Plate 21, figs. 2a, b, 8a, b

1934 Prioniodus confluens Branson & Mehl (partim) : 206, PI. 15, fig. 6, (non PI. 15, fig. j = N.

alatus) .
1934 Euprioniodina prona Huddle (partim) : 52, PI. 6, fig. 19, (non PI. 11, fig. 8 = Euprioniodina

alternata) .
1939 Prioniodus alatus Hinde ; Cooper : 404, PL 46, figs. 6, 8.
1949 Prioniodus apkanes (Cooper) Thomas : 411, PL 4, figs. 20, 34.
1949 Prioniodus obtusus Branson & Mehl ; Thomas 408, PI. 1, figs. 1, 7.
1955 Prioniodus prona (Huddle) Sannemann (partim) : 152, PL 3, fig. 1 only.
1957 Prioniodina prona (Huddle) Ziegler in Fliigel & Ziegler : 49, PL 4, fig. 6.
1 961 Neoprioniodus armata (Hinde) Scott & Collinson (partim) : 127, PL 2, fig. 24, (non

PI. 2, fig. 22 = iV. armata).

BRITISH AVONIAN CONODONT FAUNAS 159

Lectotype (here selected). The original of Branson & Mehl : 1934, 206 ; PI. 15,
fig. 6 only, University of Missouri C 365-5.

Material. 672 specimens : figured, X 264, X 263.

Range. North Crop KL i-ZLA 33, Avon Gorge K 3-C 7.

Description. The anterior denticle is tall and narrows gradually to a pointed
extremity. It is produced aborally into an aboral process. The posterior bar, which
is straight or gently down-curved, is also deflected through 45 ° and slightly twisted.
It bears a series of erect laterally compressed denticles, which are either fused or are
in close proximity. The bar is very long and may possess up to 40 denticles which
alternate in size. The basal cavity is situated at the junction of the posterior bar and
the aboral process. It has a flared lip to produce a characteristic flange.

Remarks. This is one of the most easily recognizable neoprioniodids owing to the
large aboral process of mature specimens and the cavity flange. Frequently only the
anterior denticle and cavity flange are preserved. Branson & Mehl (1934 : 206)
described two co-types of the species Prioniodus confluens (Catalogue numbers
C 365-5, University of Missouri). These appear to represent different species and
we hereby designate the specimen illustrated in PI. 15, fig. 6, as the lectotype of
Neoprioniodus confluens (Branson & Mehl). This is given the same Catalogue
Number as the other co-type (C 364-5).

One specimen (PL 21, figs, ia-c) shows extreme regularity of dentition and it is
only tentatively compared with this species.

Neoprioniodus conjunctus (Gunnell)
Plate 21, figs. i6a-i7b, 20a, b

1926 Prioniodus sp. B (Roundy) (partim) : n, PI. 4, fig. 12 only.

1 93 1 Prioniodus conjunctus Gunnell : 247, PI. 29, fig. 7.

1933 Prioniodus cacti Gunnell : 263, 265, 267, PI. 31, figs. 4 to 5.

1933 Prioniodus sp. Gunnell : 264, 267, PI. 32, fig. 32.

1941 Prioniodus conjunctus Gunnell ; Ellison : 108-111, 113, 114, PI. 20, figs. 1—3, 16.

1941 Prioniodus bulbosus Ellison : 108-111, PI. 20, figs. 4-7.

1944 Prioniodus conjunctus Gunnell ; E. R. Branson : 327.

1949 Prioniodus cacti Gunnell ; Youngquist & Downs : 169, PI. 30, figs. 16, 17.

1953 Prioniodus inclinatus Hass : 87, PI. 16, figs. 10-14.

1956 Neoprioniodus conjunctus (Gunnell) Rhodes & Miiller : 3.

1957 Prioniodina bulbosa (Ellison) Bischoff : 46, PI. 5, fig. 37.
i960 Neoprioniodus brevis Clarke : 13, 14, PI. 2, fig. 7.

1961 Neoprioniodus inclinatus (Hass) Higgins : 220, PI. 11, fig. 3.

1962 Neoprioniodus conjunctus (Gunnell) ; Higgins : 10, PI. 1, fig. 2.

Material. 7 specimens : figured, X 265, X 267, X 266.

Range. North Crop 3D 14/15, Avon Gorge Z 35-C 7.

Description. The present specimens agree perfectly with Gunnell's holotype and
with Ellison's (1961) descriptions and illustrations. The massive, blade-like anterior
denticle, with the deep posterior bar consisting of confluent, strong denticles, up to
about 4 in number, are very conspicuous features of the species. However, the

160 BRITISH AVONIAN CONODONT FAUNAS

posterior bar is strongly laterally compressed and is relatively thin, being more or less
triangular in section, with the aboral edge being the widest. The lateral faces are
flat to feebly concave. The denticles of the posterior bar are strongly laterally com-
pressed and are confluent for most of their length. They are bluntly pointed and
have more or less sharp anterior and posterior edges, their lateral faces being feebly
biconvex. The denticles proper are about twice the length of the posterior bar.
The anterior denticle is very strongly developed ; it is massive in general form, being
about five times the length and two or three times the width of the largest denticles
of the posterior bar. It is slightly recurved posteriorly, but its distal portion is more
or less straight. It has very sharp anterior and posterior edges and is so strongly
compressed in lateral view that it has a sword-like appearance. It is bluntly
pointed. Its inner aboral lateral face is very strongly extended inwards, and this is
a most conspicuous feature of the unit in lateral view. Its outer lateral face is feebly
convex to flat in the lower part and is gently convex in the upper portion. The
whole unit is very slightly curved in a horizontal plane, the inner side being feebly
concave. In aboral view the most striking feature is the wide flaring of the inner
lateral aboral edge around the junction of the anterior denticle and the posterior bar.
The outer lateral face is less conspicuously flared. The whole aboral surface below
this lateral flexure is excavated, culminating in a deep median pit which is restricted
in its area, but extends anteriorly and posteriorly as rather conspicuous longitudinal
grooves along the anterior portion of the anterior denticle and along the posterior
bar. The posterior aboral edge of the anterior denticle makes an angle of about 120 °
with the straight edge of the posterior bar. The antero-aboral corner is very slightly
convex and the junction with the edge is more or less pointed.

Neoprioniodus montanaensis (Scott)
Plate 22, figs. 5a-8b

1942 Lochreia montanaensis Scott (partim) : 289, PI. 29, fig. 9 only, PI. 40, fig. 12.

1 94 1 Prioniodus barbatus Branson & Mehl ; Ellison & Graves (partim) : 3-4, PI. 1, fig. 25

only.

1953 Prioniodus singularis Hass : 88, PI. 16, fig. 4.

1956 Prioniodus cf. singularis Hass ; Elias : 112, PI. 2, fig. 45.

1956 Prioniodus roundyi var. dividen Elias : no, PI. 2, figs. 39-41.

1957 Prioniodina alatoidea (Cooper) Bischofl : 45, PI. 5, figs. 33, 34, 36.

1957 Prioniodus sp. A Ziegler in Fliigel & Ziegler : 50, PI. 4, fig. 3.

1958 Neoprioniodus singularis (Hass) Stanley : 471, PI. 66, figs. 2, 3.
1958 Neoprioniodus sp. A Stanley : 472, PI. 66, figs. 4, 5.

1961 Neoprioniodus singularis (Hass) Higgins : PI. n, fig. 5.

1962 Neoprioniodus singularis (Hass) Higgins : PI. 1, fig. 8.

1963 Neoprioniodus singularis (Hass) Bouckaert & Higgins : 17, fig. 3.
Neoprioniodus singularis (Hass) Collinson & Druce (in press).

Material. 232 specimens : figured, X 268, X 270, X 269, X 271.

Range. North Crop CYD 6-3D 19.

Description. The most distinctive feature of this species is the long, slender,

BRITISH AVONIAN CONODONT FAUNAS 161

blade-like anterior denticle, which is enormously elongated in comparison with its
rather slight aboral process. The latter is only about one-sixth to one-seventh the
total length of the denticle. The posterior bar is also conspicuous, being short and
sharply down-curved. The denticles of the posterior bar show a sharp decrease in
length towards the posterior end of the bar. Those adjacent to the anterior denticle
tend to be greatly elongated in comparison with those that follow. All are slender,
with more or less sharp anterior and posterior edges, and gently convex lateral faces.
They are discrete for about half their length and are regularly pointed. The whole
unit is more or less strongly curved inwards in a horizontal plane.

The anterior denticle is greatly elongated and is very slender in its general form,
being bluntly to sharply pointed at its apical tip. It extends as an aboral process
only for a short distance, about one-sixth to one-seventh of its total length, below the
level of the posterior bar. The anterior and posterior edges are generally straight,
though in a few specimens they may be feebly recurved, and in other specimens there
is a very slight anterior flexure of the aboral process. The anterior denticle has
sharp anterior and posterior edges and gently convex lateral faces. It stands erect
to the anterior portion of the posterior bar. The aboral process is more or less
sharply pointed and triangular in form, without any conspicuous lateral flaring
developed on the inner aboral margin. The anterior denticle is slightly curved
inward in its distal third. The denticles of the posterior bar range from 10 to 21 in
number and show a marked decrease in size posteriorly. The 2 adjacent to the
anterior denticle are virtually confluent with it, only their apices being discrete.
The remaining denticles of the posterior bar tend to be smaller and to be inclined
more sharply posteriorly. They are discrete for about half their total length in
complete specimens. The posterior bar shows a marked decrease in depth from the
anterior to the posterior end. The posterior terminus is bluntly rounded. It has
more or less flat to gently convex lateral faces, and a sharply bevelled aboral margin
on both the inner and outer lateral faces. The whole unit is recurved inwardly in a
horizontal plane. There is a relatively inconspicuous cavity below the anterior
denticle, which extends as a shallow slit along the posterior bar and the antero-aboral
process.

Remarks. Hass (1953 : 88) erected the species Prioniodus singularis to include
the present specimens. However, because the species was illustrated and described
by Scott, even as part of a natural assemblage, it seems to us that his name must have
priority. We, therefore, regard Prioniodus singularis Hass (1953 : 88, PI. 16, fig. 4)
as a junior synonym of Scott's species.

Neoprioniodus peracutus (Hinde)
Plate 21, figs. I2a-i5b

1900 Prioniodus peracutus Hinde (partim) : 343, PI. io, fig. 22 only.

1926 Prioniodus peracutus Hinde ; Roundy : io, PI. 4, fig. 6.

1928 Prioniodus peracutus Hinde ; Holmes : 21, PI. 3, fig. 38.

1953 Prioniodus ligo Hass : 87, PI. 16, figs. 1-3.

1957 Neoprioniodus erectus Rexroad : 34, PI. 2, figs. 23, 25.

162 BRITISH AVONIAN CONODONT FAUNAS

1957 Prioniodina cassilaris (Branson & Mehl) BischofT : 46, PI. 5, figs. 27-31.

i960 N eoprioniodus peracntus (Hincle) Clarke : 14, PI. 2, fig. 6.

1964 N eoprioniodus peraculus (Hinde) Rexroad & Furnish : 674, PI. m, fig. 25.

Material. 32 specimens : figured, X 272, X 273, X 274, X 275.
Range. North Crop 3D 4-3D 22.

Description. A slender neoprioniodid in which the anterior denticle is continued
more or less vertically downward to form the aboral process. There is a slender and
highly recurved posterior bar, the straight postero-aboral portion of which makes an
angle of about 130 ° with the posterior edge of the anterior denticle. The posterior
bar decreases in depth posteriorly, its posterior termination being bluntly pointed,
its antero-aboral surfaces gently concave, and its postero-aboral surface gently
convex in lateral view. In outer lateral view its face is flat, and the whole unit is
curved slightly inward so that its inner margin is concave. The oral surface of the
posterior bar bears about 19 denticles which tend to decrease in height posteriorly.
They are basally confluent, but apically discrete, being bluntly pointed, with sharp
anterior and posterior edges and convex lateral faces. The denticles tend to be most
conspicuously discrete in the anterior third of the bar, those towards the posterior
portion being coalesced for the greater part of their length, but being discrete in their
apical region.

The anterior denticle is slightly offset inwardly from the main line of the posterior
denticles. It has sharp anterior and posterior edges, a feebly convex outer lateral
face, and a rather flat antero-inner surface which extends downwards into the flat
aboral process. The anterior edge of the aboral process is more or less straight, and
the posterior aboral edge is regularly but feebly convex, giving the whole aboral
extension a slender plough-like appearance. In inner lateral view, the inward
deflection and curvature of the anterior denticle are well seen ; the antero-aboral
face of the anterior denticle tends to be slightly concave, but otherwise the inner
lateral face is more or less flat to feebly convex in its upper portion. Its anterior
aboral edge bears two minor irregularities, but these are not sufficiently distinct to be
recognized as denticles. The interior aboral edge of the anterior denticle is
expanded, but not strongly so, and there is a very shallow longitudinal pit developed
which extends along the flattened basal surface of the posterior bar ; the anterior
part of the denticle has longitudinal slit-like grooves.

Neoprioniodus scitulus (Branson & Mehl)
Plate, 22, figs, cja-iob, 12a, b

1939 Prioniodus peracutus Cooper : 406, PI. 46, fig. 7.

1940 Prioniodus scitulus Branson & Mehl : 173, PI. 5, figs. 5, 6.

1947 Prioniodus scitulus Branson & Mehl ; Cooper : 92, PI. 20, figs. 1-3.
1949 Prioniodus spp. Youngquist & Miller : 62, PI. 101, figs. 9, 10, 14.

1956 Prioniodus scitulus Branson & Mehl ; Elias : 109, PL 2, figs. 9, 10.

*957 Neoprioniodus scitulus (Branson & Mehl) Rexroad : 35, PL 2, figs. 22, 26.
J957 Neoprioniodus striatus (Branson & Mehl) Rexroad : 35, PI. 2, figs. 11, 12.

1957 Prioniodina cassilaris Branson & Mehl ; Bischoff : 46, 47, PI. 5, figs. 27-31.

BRITISH AVONIAN CONODONT FAUNAS 163

1958 Neoprioniodus scitulus (Branson & Mehl) Rexroad : 23, 24, PI. 5, figs. 10-14.

J 959 Neoprioniodus scitulus (Branson & Mehl) Elias : 151, PI. 2, figs. 6, 7.

*959 Neoprioniodus cassilaris (Branson & Mehl) Elias : 153, PI. 2, figs. 20, 21 only.

1961 Neoprioniodus scitulus (Branson & Mehl) Higgins : 220, PI. 11, fig. 1.

1961 Neoprioniodus scitulus (Branson & Mehl) Rexroad & Burton : 1155, PI. 140, figs. 15-17.

1963 Neoprioniodus scitulus (Branson & Mehl) Bouckaert & Higgins : 17, fig. 3.

1963 Neoprioniodus scitulus (Branson & Mehl) Thompson & Goebel : 12, fig. 3.

1964 Neoprioniodus scitulus (Branson & Mehl) Rexroad & Furnish : 674, PI. 111, figs. 36, 37.

1965 Neoprioniodus scitulus (Branson & Mehl) Rexroad & Nicoll : 23, 24, PI. 2, figs. 21, 22.
Neoprioniodus scitulus (Branson & Mehl) Collinson & Druce (in press), PI. 2, fig. 1.

Material. 24 specimens : figured, X 276, X 277, X 278.

Range. North Crop 3D 2-3D 14/15.

Description. This is a variable species which, as Rexroad (1958 : 23) has
demonstrated, shows appreciable variation during ontogeny in the relative curvature
of the anterior denticle, the length of the aboral projection and the outline of the
aboral margin. The basal cavity is also variable, and tends to be filled in during
growth, ultimately resulting in a minute pit, with a longitudinal median groove
extending anteriorly and posteriorly from it. There are also smaller differences in
the form and denticulation of the posterior bar, which are shown by numbers of well-
preserved specimens in the present faunas. In younger individuals the posterior
inclination of the denticles of the posterior bar tends to be correspondingly greater
than that in older individuals, but this, as well as the other variations, seem to fall
within the limits of Branson & Mehl's species.

Remarks. The variation in " another prioniodid " mentioned by Branson &
Mehl (1940 : 174) as including a minute pit and attachment scars on the lateral faces
of the anterior denticle, seem to fall within the variation of the present species,
rather than representing a distinct species as they suggest. The most striking
general features of the present species are the long slender elegant anterior denticle,
the rather short finely pointed aboral process, and the relatively slender, straight to
slightly curved posterior bar, together with a general lack of flaring in the lateral
faces below the anterior denticle.

Neoprioniodus spathatus Higgins
Plate 21, figs. 9a, b
1961 Neoprioniodus spathatus Higgins : 217, PI. 11, figs. 2, 4, text-fig. 5.
Material, i specimen : figured, X 279.
Range. North Crop 3D 14/15.

Description. The diagnostic feature of this species is the spatulate plough-like
form of the aboral process, which projects with conspicuously concave lateral faces
and strongly laterally extended basal surfaces. It has a denticulated anterior edge.

The anterior denticle is relatively strongly developed. Its inner lateral face is flat
to very feebly convex, but its outer lateral face is more strongly convex. It has very
sharp anterior and posterior edges and is laterally twisted and slightly inwardly

i6 4 BRITISH AVONIAN CONODONT FAUNAS

recurved in its upper portion. In inner lateral view, it is concave in its anterior
proximal portion and feebly convex in its posterior proximal portion. It is elongated
and more or less sharply pointed, the anterior and posterior edges being straight.
The aboral process is strongly developed, with a concave to straight anterior margin,
and a continuously convex posterior margin. Its lateral faces are flat in the anterior
portion, but the base of the inner lateral side is strongly flared to give a conspicuously
spatulate appearance. Its anterior edge has 2 or 3 minute denticles developed on it
which are of smaller size than any on the posterior bar.

The posterior bar is short and relatively deep. It bears more than 6 denticles,
which are more or less erect or only slightly posteriorly inclined to the bar, and which
are discrete for at least half their length. They are regularly pointed and have feebly
convex lateral faces and sharp anterior and posterior edges. In outer lateral view
the whole unit is conspicuously bowed inwards. In aboral view the most conspicuous
feature is a continuous slit-like groove, which runs to the anterior aboral point of the
anterior aboral process and along its mid-line, being continued as a narrowing slit
along the posterior bar.

The posterior bar is much thinner than the aboral process but the basal groove is
not conspicuously expanded below the process. It is, however, slightly wider behind
the posterior part than it is below the anterior. The lateral aboral faces of the aboral
process are more or less straight in aboral view, the basal margin being widest below
the posterior end of the process and then curving inward sharply towards the
posterior bar. The aboral faces are more or less flat.

Remarks. Collinson & Druce (in press) include this species as a junior synonym
of N. singularis (Hass). We have only a single specimen in our collections and
we are not in a position to determine the range of morphological variation.

Neoprioniodus tulensis (Pander)
Plate 21, figs. 19a, b

1856 Prioniodus tulensis Pander (parlim) : 30, PI. 2a, fig. 1 only.
1928 Prioniodus tulensis Pander ; Holmes (partim) : 22, PI. 3, fig. 18 only.
1940 Prioniodus cassilaris Branson & Mehl : 186, PI. 6, figs. 11, 12, 15, 17.
1950 Prioniodus cassilaris Branson & Mehl ; Youngquist, Miller & Downs : 528, PL 67,
figs. 23, 24.
non 1957 Prioniodina cassilaris (Branson & Mehl) Bischoff : 47, PI. 5, figs. 38, 39 ( = N.
peracutus) .
1963 Neoprioniodus tulensis (Pander) Rexroad & Collinson : 18, PI. 2, fig. 17, 22, 23.

Material. 5 specimens : figured, X 280.

Range. North Crop CYD 6-CYD 7.

Description. The distinctive feature of the present specimens is the long,
recurved, bluntly pointed anterior denticle, the broad spatulate form of the aboral
process, and the elongated posterior bar, which bears a series of about 15 denticles
on its oral surface. These denticles are discrete for most of their length, and decrease
in size posteriorly.

BRITISH AVONIAN CONODONT FAUNAS 165

The anterior denticle is elongated, wide and bluntly pointed. It is gently recurved
in its distal half, but its proximal half stands only slightly inclined to the anterior
portion of the posterior bar. It has sharp anterior and posterior edges and very
feebly convex lateral faces, the outer distal lateral face being almost flat.

The aboral process is broad in relation to its length. Its anterior edge is a con-
tinuation of the anterior edge of the anterior denticle, and it is more or less straight.
Its anterior aboral termination is bluntly rounded and its posterior aboral edge is
strongly convex. It has flat lateral faces.

The posterior bar is elongated, and has a concave proximal portion and a relatively
straight distal portion when seen in outer lateral view. It decreases in depth
posteriorly and bears about 15 denticles ; those of the median third tend to be the
largest and they decrease posteriorly in size ; they are basally confluent but are
discrete for most of their length, with sharp anterior and posterior edges and gently
convex lateral faces. There is a tendency in the median part of the bar for a
hindeodellid type of denticulation, but this is not a conspicuous feature of the unit.
The outer lateral face of the posterior bar is flat and shows a very slight bevelled
ridge parallel to its aboral surface. The whole unit is gently incurved in a horizontal
plane, so that its inner lateral face is concave. The denticles of the posterior bar
stand more or less erect to the bar itself.

In inner lateral view the anterior denticle is much more strongly curved and the
curvature is especially strongly developed on the posterior proximal lateral face.
The inner aboral longitudinal edge of both the aboral process and the posterior bar
are sharply bevelled and the inner lateral curvature of both the anterior denticle and
the posterior bar are conspicuous.

The aboral surface is marked by a shallow pit below the anterior denticle, which is
extended posteriorly as a very narrow slit-like cavity. The basal cavity also extends
anteriorly as a narrow slit-like process, running along the median part of the anterior
aboral surface. The basal cavity itself is not conspicuously laterally expanded.
There is a strong bevelled flange on the inner aboral edge of the anterior aboral
process. The strongest lateral curvature of the posterior bar occurs in its anterior
half, the posterior part being more or less straight.

Remarks. The only substantial difference between the present species and N.
scitulus (Branson & Mehl) is the longer posterior bar of the present specimens, which
bears a greater number of denticles. There seems to be a morphological discon-
tinuity between the two, but we are not certain about this and further study may
indicate that the two are morphologically continuous and that N. scitulus should be
regarded as a junior synonym of N. tulensis.

Neoprioniodus varians (Branson & Mehl)
Plate 21, figs. 18a, b

1940 Prioniodus varians Branson & Mehl : 174, PI. 5, figs. 7, 8.

1941 Prioniodus barbatus Branson & Mehl ; Ellison & Graves : 3, 4, PI. 1, fig. 27 only.
1957 Prioniodina varians (Branson & Mehl) Bischofi : 49, PI. 5, fig. 35.

1957 Prioniodina varians (Branson & Mehl) Ziegler in Fliigel & Ziegler : 50.

166 BRITISH AVONIAN CONODONT FAUNAS

1957 Neoprioniodus varians (Branson & Mehl) Rexroad : 35, PI. 2, fig. 10.

1958 Neoprioniodus varians (Branson & Mehl) Rexroad : 24, PI. 5, figs. 3, 4.

1961 Neoprioniodus varians (Branson & Mehl) Rexroad & Burton : 1155, PI. 140, figs. 9,

10.
1965 Neoprioniodus varians (Branson & Mehl) Rexroad & Nicoll : 24, PI. 2, fig. 18.

Material. 7 specimens : figured, X 281.

Range. North Crop CYD 7-3D 17.

Description. The present specimens have a conspicuous and relatively short
anterior denticle, which is very wide at its base in comparison with its length. It is
regularly tapered, its anterior and posterior edges being straight, and its distal tip
pointed. Its inner lateral face is strongly convex in the proximal portion and less
strongly convex in the distal portion. It is extended aborally as a very short aboral
process, with a straight anterior edge and a continuously concave posterior edge,
which is continuous with the concave margin of the posterior bar when viewed in
lateral view. Its inner lateral face is only feebly convex, and there is no sharp inner
basal flexure.

The posterior bar, when seen in inner lateral view, is continuously and relatively
strongly curved downward. It decreases in depth posteriorly and its posterior
aboral corner is bluntly rounded. Its lateral face is strongly convex in the anterior
half, but flat to feebly convex in the posterior part, its basal margin being slightly
bevelled. Its oral surface bears about 16 large denticles, between which there are
some smaller " germ " denticles developed, especially in the anterior third. The
denticles as a whole are closely crowded, but the major denticles are generally not
confluent with one another. The denticles in the median half of the bar tend to be
rather larger in size than the rest. The denticles on the posterior quarter of the bar
are the smallest. All the denticles stand more or less erect to the basal surface
below them, and have sharp anterior and posterior edges and convex lateral faces.
They are short and bluntly pointed.

The anterior denticle stands erect to the oral surface of the posterior bar in contact
with it. It is also gently curved inward along its length.

In outer lateral view, there is a very conspicuous bevelled edge along the whole of
the aboral margin. The outer lateral face of the anterior denticle and the aboral
process is more or less flat in the lower proximal portion, but becomes gently convex
in the distal two-thirds. The curvature of the posterior bar is very conspicuous, and
the bar decreases in depth posteriorly. In lateral view the anterior end of the aboral
process is slightly flexed outward in a horizontal plane, and the main part of the
posterior bar is gently flexed inward, so that its inner lateral face is concave. There
is a deep and obvious basal cavity below the posterior part of the anterior denticle,
which decreases in width but is continued as a rather wide extension along both the
aboral process and the posterior bar.

Neoprioniodus sp. nov. A
Plate 22, fig. 14
Material, i specimen : figured, X 282.

BRITISH AVONIAN CONODONT FAUNAS 167

Range. North Crop 3D 17.

Description. This species is marked by the lack of a large aboral process and
the presence of a wide flaring basal cavity. The anterior denticle is strongly laterally
compressed, fairly short and recurved in its aboral third. The posterior bar is deep
and relatively short, bearing a series of 14 fused, laterally compressed, needle-like
denticles, which are inclined posteriorly. In aboral view the pit is large and sub-
apical, having flaring lips. It runs along the posterior bar as a narrowing cavity
terminating at the posterior extremity of the posterior bar.

Neoprioniodus cf. armatus (Hinde)
Plate 21, figs. 3a-c
1879 Prioniodus armatus Hinde (partim) : 360, PL 15, fig. 20, non fig. 21.

Material. 3 specimens : figured, X 283.

Range. North Crop ZLA 14.

Description. The anterior denticle is tall and laterally compressed. The
anterior edge is feebly concave in lateral view, with a sharp anterior and posterior
edge. The blunt aboral surface projects slightly aborally. The posterior bar is
denticulate, curved inward, and slightly twisted. The fused denticles are small,
more or less erect, number about 11, and decrease in height posteriorly. The cavity
is small and situated postero-aborally of the anterior denticle.

Remarks. This form appears to be very close to Neoprioniodus armatus (Hinde
1879, PI- z 5> n S- 20 ) which is most abundant in the Upper Devonian. This species
probably has a long range, and the present specimens may well belong to it but
because of their limited occurrence, both stratigraphically and numerically, we have
not made a direct assignation. Hinde's fig. 21 probably represents a different
species.

Neoprioniodus cf. camurus Rexroad
Plate 22, figs. ia-4b
!957 Neoprionodus camurus Rexroad : 33, PI. 2, figs. 18-20.
Material. 10 specimens : figured, X 284, X 285, X 286, X 287.
Range. North Crop 3D 14/15.

Description. The distinctive features of this species are the relatively elongated
posterior bar, the sharp inner lateral curvature of the bar immediately posterior to
the anterior denticle, and the slender anterior denticle and aboral process.

The posterior bar is more or less straight in inner lateral view, and is relatively
shallow. Its oral surface bears up to 18 denticles, some of which are separated by
smaller germ denticles. The denticles are confluent for most of their length, and
only their apices are discrete. The apices are sharply pointed with sharp anterior
and posterior edges and gently convex lateral faces ; those in the posterior quarter

n.S

BRITISH AVONIAN CONODONT FAUNAS

stand more or less erect to the basal surface of the bar, but those in the anterior three-
quarters are inclined slightly anteriorly. The denticles are of variable height but
there is no conspicuous increase or decrease in height in either direction. There is a
slight tendency for the two denticles immediately posterior to the anterior denticle to
be larger than the rest. The anterior denticle, which is not conspicuously large, is
flexed sharply inwards, so that its inner lateral edge points inwardly and anteriorly,
making an angle of about 140 ° with the posterior bar. When seen in inner lateral
view, looking directly at the junction between the anterior denticle and the posterior
bar, the angle between the posterior edge of the aboral process and the posterior bar
is about 70 °. The anterior denticle is more or less straight, with sharp and straight
anterior and posterior edges and gently convex lateral faces.

The aboral process is relatively short in comparison with the length of the denticles,
with a rather sharp aboral point, and straight anterior and posterior edges.

In outer lateral view the most conspicuous feature of the unit is the sharp lateral
recurvature at a point about two or three denticles posterior to the anterior denticle.
There is a faintly perceptible longitudinal bevelled edge developed, but the whole
aboral surface of the unit is rather thin, although it is excavated by a longitudinal
slit. There is a shallow, little-flared, posterior cavity below the posterior margin of
the anterior denticle.

Genus OZARKODINA Branson & Mehl 1933
1933 Ozarkodina Branson & Mehl 51.
Type species. Ozarkodina typica Branson & Mehl.

Ozarkodina curvata Rexroad
Plate 27, fig. 6

1958 Ozarkodina curvata Rexroad
1 96 1 Ozarkodina curvata Rexroad

1964 Ozarkodina curvata Rexroad

1965 Ozarkodina curvata Rexroad
Ozarkodina curvata Rexroad

24, PI. 4, figs. 1-3.

Rexroad & Burton : 1156, PI. 141, figs. 13, 14.
Rexroad & Furnish : 674, PI. in, figs. 10, 11.
Rexroad & Nicoll : 25, PL 2, figs. 1, 2.
Collinson & Druce (in press).

Material, i specimen : figured, X 289.

Range. North Crop CYD 7.

Description. The most conspicuous feature of this species is the short, strongly
depressed anterior bar, which bears a series of about 4 denticles on its oral edge.
These are basally confluent, and only their apices are discrete, being sharply pointed,
with gently convex lateral faces. They tend to be recurved parallel to the apical
denticle, and show a more or less constant decrease in size anteriorly, those adjacent
to the apical denticle being the largest. The anterior bar is relatively deep and
relatively straight ; its anterior end is bluntly spatulate and its outer lateral face
more or less flat. There is a rather flat bevel visible along the whole aboral edge of
the unit, when seen in outer lateral view. The base of the apical denticle is about

BRITISH AVONIAN CONODONT FAUNAS

169

two to three times as wide as the largest denticles adjacent to it, and is confluent with
them. It is recurved posteriorly but has a more or less straight posterior edge and is
bluntly pointed. It has sharp anterior and posterior edges. Its outer lateral face is
feebly convex, and the basal margin is sharply, but not greatly, outflexed below it to
give a rather inconspicuous navel. The posterior bar is about twice the length of the
anterior, but is less deep. It is straight along its aboral margin and the distal end
makes an angle of about 90 ° with the distal end of the anterior bar. The posterior
bar decreases in depth posteriorly and bears a series of crowded confluent denticles,
more or less of similar size. These number up to about 11 or 12, and have rather
sharply pointed free tips. They show no overall trend in size, but the posterior ones
tend to be slightly smaller than the rest. Germ denticles are visible between some of
them. Those near the anterior end of the posterior bar tend to be inclined posteri-
orly, but those towards the distal end of the bar stand more or less erect to the base
of the bar itself. The whole posterior bar is sharply inflexed at about its mid-length,
so that its inner lateral face is longitudinally concave. The posterior aboral corner
of the unit is sharply rounded. In inner lateral view, the inward curvature of the
unit is a very conspicuous feature.

There is a small basal cavity below the posterior edge of the denticle, around which
the basal margins flare slightly. This is continued as a conspicuous but narrow slit
along the anterior and posterior bars.

Ozarkodina cotnpressa Rexroad
Plate 27, fig. 23

1957 Ozarkodina compressa Rexroad :

1958 Ozarkodina compressa Rexroad ;
1961 Ozarkodina compressa Rexroad ;

1964 Ozarkodina compressa Rexroad ;

1965 Ozarkodina compressa Rexroad ;

36, PI. 2, figs. 1, 2.

Rexroad : 24, PI. 6, figs. 1, 2.

Rexroad & Burton : 1156, PI. 141, figs. 16, 17.

Rexroad & Furnish : 674, PI. in, fig. 9.

Rexroad & Nicoll : 24, 25, PI. 2, figs. 3, 4.

Material. 12 specimens : figured, X 420.

Range. Avon Gorge C 3-S 49, North Crop 3D 14/15-3D 22.

Description. The present specimens are broadly similar to those described by
Rexroad and other authors, although they differ slightly in that the posterior bar

Denticles

Apical denticle

Posterior

Posterior bar

Anterior bar

Lip of basal cavity
Fig. 33. Ozarkodina sp. showing morphological terms used in the text.

170 BRITISH AVONIAN CONODONT FAUNAS

tends to be rather more elongate and is slightly twisted. This distinction does not
seem sufficient, however, to warrant their recognition as a different species, and in
other aspects of their denticulation and general form they closely resemble Ozarkodina
compressa.

Ozarkodina delicatula (Stauffer & Plummer)
Plate 27, figs. 15, 19

1932 Bryantodus delicatulus Stauffer & Plummer : 29, PI. 2, fig. 27.

1932 Bryantodus nasuius Stauffer & Plummer : 29, PI. 2, fig. 28.

1932 Bryantodus sulcatus Stauffer & Plummer : 30, PI. 2, figs. 11, 14, 30.

1933 Bryantodus delicatus Gunnell : 267, PI. 32, fig. 43.
1933 Bryantodus rugosus Gunnell : 269, PI. 32, fig. 44.
1933 Bryantodus stritatus Gunnell : 268, PI. 32, fig. 45.
1933 Bryantodus strigillatus Gunnell : 268, PI. 32, fig. 46.

non 1933 Bryantodus delicatus (Stauffer & Plummer) Branson & Mehl : 222, PI. 16, fig. 19.
1941 Ozarkodina delicatula (Stauffer & Plummer) Ellison : 120, PI. 20, figs. 40-42, 47.
1 94 1 Ozarkodina delicatula (Stauffer & Plummer) Ellison & Graves : 3, PI. 1, figs.

12-14.
1944 Ozarkodina delicatula (Stauffer & Plummer) E. B. Branson : 327.

1948 Ozarkodina delicatula (Stauffer & Plummer) Youngquist & Heezen : 771, PI. 118,
fig. 6.

1949 Ozarkodina delicatula (Stauffer & Plummer) Youngquist & Downs : 168, PI. 30,
figs. 1, 3, 7, 11.

non 1949 Bryantodus delicatus (Stauffer & Plummer) Beckmann 161, PI. 1, fig. 7 ; PI. 3,

fig- 3-
1952 Ozarkodina delicatula (Stauffer & Plummer) Rhodes : 893, PI. 126, figs. 2, 3.

1957 Ozarkodina delicatula (Stauffer & Plummer) Bischoff : 39, PI. 1, figs. 25-28.

1958 Ozarkodina compressa Rexroad (partim) : 24.

1961 Ozarkodina delicatula (Stauffer & Plummer) Higgins : 220, PI. 12, fig. 13.

1961 Ozarkodina delicatula (Stauffer & Plummer) Rexroad & Burton : 1156, PI. 141,

fig. 12.
1963 Ozarkodina delicatula (Stauffer & Plummer) Bouckaert & Higgins : 17, fig. 3.

Ozarkodina delicutula (Stauffer & Plummer) Collinson & Druce (in press).

Material. 27 specimens : figured, X 290, X 291.
Range. North Crop CYD 7-3D 20.

Description. This is a relatively variable species with the following character-
istics. Anterior and posterior bars are thin, blade-like, straight or continuously
gently arched, the anterior tending to be the deeper and the longer. Denticles
closely spaced, more or less sub-equal, discrete only at their pointed apical ends.
Apical denticle is from one and a half to three times the width of the adjacent
denticles. It has a slightly flared basal cavity.

The anterior bar is of more or less uniform depth and has a straight to gently
concave aboral edge. It bears 12 to 14, strongly laterally compressed denticles,
which are confluent for most of their length only their apical tips being discrete.
These are sharply pointed, with sharp anterior and posterior edges which are straight.
The anterior bar itself is about equal in depth to the length of the denticles. The

BRITISH AVONIAN CONODONT FAUNAS 171

denticles at the anterior end of the bar are more or less erect, but those toward the
posterior end become increasingly strongly inclined posteriorly. In a few specimens
the denticles at the anterior end of the bar are also posteriorly inclined. The lateral
faces of the anterior bar are flat to gently convex, the convexity increasing in the
posterior half of the bar. The apical denticle is variable in size and in inclination.
It is of similar form to the denticles of the anterior bar and its free portion is sharply
pointed, with sharp, straight anterior and posterior edges. It is strongly inclined at
an angle of up to about 50° to the posterior bar, and is from one and a half to three
times as wide and about twice as long as the largest adjacent denticles. In some
specimens the denticles of the anterior bar are more widely spaced and appear almost
discrete, but in most specimens they are more or less confluent.

The posterior bar is depressed with respect to the anterior, and the whole aboral
surface is either continuously and gently concave, or both the anterior and posterior
bars may be more or less straight and meet at an angle of about 120 °. (This is the
projected angle made by their straight distal ends in those specimens where the lower
surface is strongly arched). The posterior bar bears 10 or more laterally compressed
closely spaced denticles, which, although in some specimens they are more or less
equal in size, show a marked decrease in size in the posterior quarter of the bar in
others. They are generally rather smaller than the denticles of the anterior bar and
fewer in number. In some specimens the posterior bar, and to a lesser extent the
anterior bar, are strongly flexed inwards. The denticles of the posterior bar are all
inclined at about 50 ° to the posterior bar itself.

In aboral view the unit has a rather conspicuously flattened aboral margin, which
decreases in width towards the anterior and posterior ends of the unit. There is a
continuous longitudinal slit along both limbs, and a slightly flared median cavity
below the apical denticle, which is continuous with the slit. The flaring of this cavity
is not a conspicuous feature, but the thickened lips of the main longitudinal cavity
are more or less conspicuous in aboral view.

This species shows some variation in the degree of flexing of the anterior and
posterior bars in a vertical plane and in the relative depth and detailed denticulation
of the anterior bar. Specimens illustrating various morphological variations are
illustrated.

Ozarkodina hindei Clarke
Plate, 27 figs. 16, 17, 22

1879 Polygnathus dubius Hinde : 363, PI. 16, fig. 8 only.

1900 Polygnathus dubius Hinde ; Hinde : 341, PI. 9, fig. 1 only.

1928 Prioniodina (Polygnathus) dubius (Hinde) Holmes : 19, PI. 8, fig. 1 only.

i960 Ozarkodina hindei Clarke : 18, PI. 3, figs, i, 6.

1961 Ozarkodina compressa Rexroad ; Rexroad & Burton : PI. 141, fig. 16 only.

Material. 3 specimens : figured, X 294, X 293, X 295.

Range. North Crop 3D 6-3D 12.

Description. The diagnostic features of this species are the very deep and
strongly laterally compressed anterior and posterior bars, and the very wide, short

172 BRITISH AVON1AN CONODONT FAUNAS

and conspicuously pointed apical denticle. The anterior bar is deeper than the
posterior, and carries from 4 to 6 denticles on its oral edge. These are very strongly
laterally compressed and more or less sharply recurved, being confluent for the
greater part of their length. Their apical halves are discrete, and they are sharply
pointed with straight anterior and posterior edges, the anterior edge tending to be
sharply deflected at an angle of about 130 ° at or near the point of confluence with the
adjacent denticles, but the posterior edge being straight throughout its length.
Germ denticles are visible in places on the anterior bar, especially at its junction
with the apical denticle. The most posterior denticle of the apical bar is so coalesced
with the anterior edge of the apical denticle that only its highest portion is discrete.
The anterior bar tends to show a slight increase in depth anteriorly ; the denticles in
the posterior two thirds of the bar are of more or less uniform height. There may,
however, be 1 or 2 much smaller blunt denticles present on the spatulate anterior end.
The denticles may curve slightly inwardly in some specimens. The inner lateral face
of the anterior bar is more or less flat, but the outer lateral face has a conspicuous,
shoulder-like thickening near the base of the denticles. The anterior bar tapers
sharply towards the aboral margin.

The apical denticle is at least three times as wide as the largest denticles of the
anterior and posterior bars. It is very sharply pointed, and is only about twice as
long as its basal width. It is recurved posteriorly at an angle of about 60 ° to the
posterior bar, and germ denticles are conspicuous at its base. There is a feebly
flaring protrusion of the basal margin below its posterior margin.

The posterior bar is shorter and shallower than the anterior, and bears up to 9
denticles of more or less uniform height, basally confluent, but their apices discrete
and sharply pointed. They tend to be very slightly smaller than those of the larger
series of the anterior bar. The posterior bar thickens towards its aboral surface,
which is wide and flat, as an extension of the basal cavity below the apical denticle.
It decreases in both width and depth posteriorly, however, and its posterior aboral
margin is bluntly rounded. Its inner lateral face is more or less flat and the posterior
denticles are gently inclined to the base of the posterior bar. The posterior bar and
the anterior bar have relatively straight aboral margins and they make an angle of
about 130 ° with one another in a vertical plane.

The whole unit is strongly bowed laterally in a horizontal plane so that it is concave
on the inner side, and the denticles are also incurved to a varying degree. This is
especially true of the apical denticle. The anterior edge of the anterior bar has an
acute angle at the anterior aboral margin and is inclined sharply posteriorly, with a
faintly serrated anterior edge in some specimens. In outer lateral view the lateral
faces of the unit are flat to gently convex, and the inner curvature is a conspicuous
feature. In most specimens there is developed to a varying intensity a bevelled
aboral margin, especially conspicuous in the median half of the unit, which includes
the posterior part of the anterior bar and the anterior part of the posterior bar. The
outer lateral view of the navel below the posterior edge of the apical denticle is
distinct and forms a rather flattened apical area.

In aboral and outer lateral views the basal cavity is a conspicuous feature, partic-

BRITISH AVONIAN CONODONT FAUNAS 173

ularly so in outer view. There is a strong basal expansion below the posterior edge
of the apical denticle, and in the anterior third of this, the basal cavity is deepest and
widest, forming a biconvex pit. It is extended anteriorly and posteriorly as a shallow
slit-like groove, but the posterior extension becomes indistinct near the posterior end
of the margin of the expanded base. The anterior extension continues towards but
does not quite reach the anterior end of the anterior blade.

Remarks. This species is close to 0. compressa Rexroad, but differs from it in the
shorter and deeper anterior and posterior bars and the short and relatively very
broad apical denticle.

Ozarkodina macer (Branson & Mehl)

Plate 27, figs. 7, 8

1934 Bryantodus macer Branson & Mehl : 283, PI. 23, fig. 4.

1934 Ozarkodina elongata E. R. Branson : 313, PI. 28, fig. 25.

? 1934 Bryantodus scitulus Branson & Mehl : 283, PI. 23, fig. 5.

1943 Bryantodus equalis Cooper in Cooper & Sloss : 170, PI. 29, fig. 9.

1943 Bryantodus cf. planus Branson & Mehl ; Cooper in Cooper & Sloss : 170, PI. 29,

fig- 3-
1943 Ozarkodina regularis Branson & Mehl ; Cooper in Cooper & Sloss : 170, PI. 29, fig. 12.
1943 Subbryantodus grandis Cooper in Cooper & Sloss : 175, PL 29, fig. 19.
1949 Ozarkodina cf. elongata Branson & Mehl ; Thomas : 411, PI. 4, fig. 28.
1955 Ozarkodina regularis Branson & Mehl ; Sannemann : 133, PI. 6, fig. 5 only.
1957 Ozarkodina willsi Rhodes & Dineley : 364, PI. 38, figs. 1, 5.
1957 Ozarkodina firma (Stauffer) Rhodes & Dineley : 364, PI. 27, fig. 20.
1957 Ozarkodina delicatula (Stauffer & Plummer) Bischoff : 39, PI. 1, figs. 25-28.
1957 Ozarkodina roundyi (Hass) Bischoff : 40, PI. 2, fig. 2 only.

1957 Ozarkodina congesta Stauffer, Bischoff & Ziegler : 75, 76, PI. 12, figs. 18-20, PI. 13,
fig. 14.

1958 Ozarkodina tortilis Tatge ; Huckriede : 154, PI. n, fig. 26 only.

!959 Ozarkodina cf. delicatula (Stauffer & Plummer) Helms : 646, PI. VI, figs. 14-16.
x 959 Ozarkodina cf. regularis Branson & Mehl ; Helms : 647, PL IV, figs. 13, 14, (non PL

IV, fig. 15 = 0. cf. congesta).
i960 Ozarkodina regularis Branson & Mehl ; Zimmermann : PL IX, fig. 11 only.
i960 Ozarkodina media Walliser ; Spasov : 68, PL 1, fig. 10 only.

Material. 71 specimens : figured, X 304, X 305.

Range. Avon Gorge K 8-Z 38.

Description. A gently arched blade with asymmetrical anterior and posterior
blades, commonly bearing 5 to 7 straight, posteriorly inclined denticles on the
anterior blade, and 8 to 12 straight posteriorly inclined denticles on the posterior
blade. The denticles of the anterior and posterior blades may be of uniform eleva-
tion, highest near the apical denticle and decreasing in elevation to the extremities of
the blades, or they may be of variable elevation. The apical denticle is straight to
slightly curved, posteriorly inclined and higher and wider than the blade denticles.
The small circular basal cavity is situated beneath the apical denticle. The aboral
edge is sharp.

174 BRITISH AVONIAN CONODONT FAUNAS

Remarks. Ozarkodina macer (Branson & Mehl) as here denned, includes a group
of ozarkodinids which are characterized by having asymmetrical anterior and
posterior limbs. The outline of the denticles of both the anterior and posterior
blades is similar in lateral view. 0. macer resembles 0. cf. congesta in the outline of
the blades in lateral view, but in 0. macer the anterior and posterior limbs are
asymmetrical whereas in 0. cf. congesta they are symmetrical.

Compared with Ozarkodina macra the blade of Ozarkodina macer is thinner.

Ozarkodina macra Branson & Mehl
Plate 27, figs. 12, 20, 21

? 193 1 Bryantodus equalis Cooper : 234, PI. 28, fig. 9.

? 1931 Bryantodus subequalis Cooper : 234, PI. 28, fig. 11.

1934 Ozarkodina macra Branson & Mehl : 192, PI. 17, fig. 5.

1934 Ozarkodina regularis Branson & Mehl : 287, PI. 23, figs. 13, 14.
? 1938 Ctenognathus firmus Stauffer : 425, PI. 48, figs. 2, 6, 15.

1955 Ozarkodina regularis Branson & Mehl ; Sannemann : 133, PI. 6, figs. 3, 7 only.
? 1956 Ozarkodina rhenana Bischoff & Ziegler : 153, PI. 14, fig. 19.
? 1957 Ozarkodina ballai Bischoff & Ziegler : 74-75, PI. 13, figs. 1, 2.

1957 Ozarkodina macra Branson & Mehl ; Bischoff & Ziegler : 77, PI. 12, figs. 13a, b, PI. 13,
figs. 10a, b.

1957 Ozarkodina cf. macra Branson & Mehl ; Bischoff & Ziegler : 78, PI. 13, fig. 11, PI. 19,
fi g- 43

Material. 36 specimens : figured, X 296, X 298, X 297.

Range. Avon Gorge K 2-Z 18, North Crop KL 2-KL 16.

Description. The aboral edge in lateral view is slightly arched. The anterior
and posterior blades are of almost equal length, and bear 8-12 straight, posteriorly
inclined denticles, fused for the greater part of their length but free at their tips. The
anterior blade is thicker than the posterior blade. The apical denticle is two to three
times as wide as the denticles of the anterior and posterior blade. It is inclined to the
posterior at an angle of 70 °. The small circular basal cavity is situated immediately
beneath the apical denticle and the aboral edge is sharp.

Ozarkodina parva (Huddle)
Plate 27, fig. 18

1934 Bryantodus parvus Huddle : 74, 75, PI. 4, fig. 9.

1939 Bryantodus orthus Cooper : 385, PI. 43, figs. 33, 34.

J 939 Subbryantodus ? scitulus (Branson & Mehl) Cooper : 417, PI. 43, figs. 35, 36.

Material. 107 specimens : figured, X 299.

Range. Avon Gorge K 3-C 7, North Crop KL 2-ZLA 32.

Description. The blade is short, thin, symmetrical and slightly arched. The
apical denticle is subcentral, flattened, sharp edged and acutely pointed to the poster-
ior. The blade denticles are closely appressed and similar to the apical denticle in
outline, inclination and insertion. They number 7 to 12 on each side of the apical

BRITISH AVONIAN CONODONT FAUNAS 175

denticle, are fused for the greater part of their length, and are highest near the apical
denticle. They decrease in height uniformly to the anterior and posterior extremi-
ties. The basal cavity is small and thin, and is situated beneath the apical denticle.

Ozarkodina plana (Huddle)
Plate 27, figs. 1-3

1934 Bryantodus planus Huddle : 75-76, PI. 10, fig. 8.

non 1934 Bryantodus planus Huddle ; Branson & Mehl : 284, PI. 23, fig. 8.

1957 Ozarkodina cf. O. plana (Huddle) Rhodes & Dineley : 364, PI. 37, fig. 24.

1961 Ozarkodina plana (Huddle) Scott & Collinson : 128, PI. 2, fig. 8.

Material. 12 specimens : figured, X 300, X 301, X 419.

Range. Avon Gorge K 3-Z 15.

Description. The anterior and posterior blades are short, slightly arched,
laterally compressed, and very thin. The apical denticle is short, broad at the base,
acutely pointed and situated slightly anterior to the basal cavity. The blade
denticles are similar in outline to the apical denticle and usually number 4 anteriorly
and 6 posteriorly. The basal cavity is small and situated slightly anterior to the
apical denticle.

Ozarkodina plumula Collinson & Druce
Plate 27, figs. 4, 5

Ozarkodina plumula Collinson & Druce (in press).
Material. 4 specimens : figured, X 302, X 303.
Range. North Crop 3D 12.

Description. The diagnostic characteristic of this species is the slender elon-
gated anterior bar, bearing a large number of small, posteriorly inclined denticles.
The posterior bar is shorter and deeper, and bears a smaller number of conspicuously
larger denticles than those of the anterior bar. The apical denticle is only slightly
larger than the largest of the posterior bar and the whole unit is more or less con-
tinuously recurved. The anterior bar is of slender elongate construction, relatively
shallow in depth, and bears a series of up to 12 small confluent denticles, only the
apical tips of which are discrete. These are sharply inclined to the anterior bar and
tend to decrease in size posteriorly.

The apical denticle is only slightly larger than those adjacent to it both in length
and in width. It is, however, conspicuously more sharply inclined than most of
those of the anterior bar, and in this it parallels the denticles of the shorter posterior
bar. It is very strongly laterally compressed, with sharp anterior and posterior
edges, and is confluent with the posterior denticles for the greater part of its posterior
margin, though its inclination removes most of its anterior edge on the adjacent
anterior denticles.

The denticles of the posterior bar are similar to, but rather larger than, those of the

176 BRITISH AVONIAN CONODONT FAUNAS

anterior. They are about 5 or 6 in number and are strongly laterally compressed
with sharp anterior and posterior edges and gently biconvex lateral faces. Their
bases are confluent and their sharply pointed apices discrete. The posterior bar is
deeper than the anterior, and tends to become shallower towards its posterior end.
It is inclined to the anterior bar at an angle which varies from I30°-I40°, although
the junction between the two is continuously curved, so that the whole aboral
margin is concave with more or less straight distal ends.

There is a relatively inconspicuous flare on the basal margin below the posterior
edge of the apical denticle. The basal cavity is gently flared, being slightly larger
than that of many typical ozarkodinids. It is continued as a longitudinal slit along
both the anterior and the posterior bars, both of which become narrower towards the
aboral margin. The whole unit is more or less straight in a vertical plane.

In complete specimens the denticles are seen to be sharply pointed, and the
denticles of the posterior bar are discrete for a greater part of their length than those
of the anterior bar. The posterior aboral corner of the posterior bar is very strongly
rounded and terminates orally in the tip of the posterior denticle.

Ozarkodina cf. congesta Stauffer

Plate 27, fig. 13

1940 Ozarkodina congesta Stauffer : 427, PI. 59, fig. 12.

1957 Ozarkodina plana Huddle ; Bischoff & Ziegler 78, 79, PI. 12, fig. 15a, b.

1959 Ozarkodina cf. regularis Branson & Mehl ; Helms : 647, PI. IV, fig. 15 only.

Material. 14 specimens : figured, X 288.

Range. Avon Gorge Z 17-Z 37.

Description. A gently arched unit with symmetrical anterior and posterior
blades, commonly bearing 7 straight posteriorly inclined denticles, highest near the
apical denticle, and decreasing in length uniformly to the anterior and posterior
extremities of the blades. The apical denticle is straight to slightly curved,
posteriorly inclined and higher and wider than the blade denticles. The small
circular basal cavity is situated beneath the apical denticle, The aboral edge is
sharp.

Remarks. In the Z beds of the Avon Gorge, specimens of Ozarkodina are found,
which are neither identical with one another nor with previously described species.
Reference to the literature shows that previous workers, for example Helms (1959)
and Bischoff & Ziegler (1957), have often assigned specimens in their studies to
species where the holotype bears little resemblance to their specimens. In the
present study, the majority of the Z bed ozarkodinids have been referred to two
general categories ; 0. cf. congesta Stauffer, which has symmetrical anterior and
posterior limbs, and Ozarkodina macer (Branson & Mehl) which has asymmetrical
anterior and posterior limbs.

BRITISH AVONIAN CONODONT FAUNAS 177

Ozarkodina cf. delicatula (Stauffer & Plummer)
Plate 27, fig. 14

1932 Bryantodus delicatula Stauffer & Plummer 29, PI. 2, fig. 27.

Material. 12 specimens : figured, X 292.

Range. North Crop ZLA 31-ZLA 33.

Description. The unit is bowed and slightly curved. Both bars are long. The
anterior bar bears about 8 denticles which are sub-equal, laterally compressed, fused
at their bases with free chevron tips, and all are inclined posteriorly. The antero-
aboral edge is bluntly spatulate. The apical denticle is largest, fairly short, about
twice the size of those of the anterior bar, laterally compressed and inclined
posteriorly. The posterior bar is of equal length to the anterior bar, but less deep,
and shallows posteriorly. The denticles are similar and about 8 in number. The
basal cavity is minute and restricted to the aboral region of the apical denticle with
sometimes feebly flaring lips.

Remarks. Stauffer & Plummer (1932 : 29), described 0. delicatula from Penn-
sylvanian strata, and it has been recognized in Upper Visean and Namurian rocks
(Bischoff 1957, Higgins 1961). The present specimens appear to be very similar to
the type specimens, and it is possible that the species has an even longer range than
previously thought.

Ozarkodina cf. elegans (Stauffer)

Plate 27, fig. 24

1938 Ctenognathus elegans Stauffer : 425, PI. 48, figs. 9, 12.

1940 Ctenognathus elegans Stauffer ; Stauffer : 422, PI. 59, figs. 3-5, 8.

1955 Ozarkodina elegans (Stauffer) Sannemann : 133, PI. 6, fig. 9.

1956 Ozarkodina denckmanni Ziegler : PI. 7, figs. 1, 2, PI. 6, figs. 30, 31.

1957 Ozarkodina elegans (Stauffer) Bischoff & Ziegler : 76, PI. 20, figs. 29-33.

1958 Ozarkodina denckmanni Ziegler ; Bischoff & Sannemann : 99, PI. 14, figs. 22, 23.
i960 Ozarkodina regularis Branson & Mehl ; Zimmermann : PI. IX, fig. 10.

1961 Ozarkodina delicatula (Stauffer & Plummer) Rexroad & Burton : 1156, PI. 141,

fig. 12.
1963 Ozarkodina media Walliser ; Spasov & Veselinovic : 246, PI. 1, fig. 14 only.

Material. 2 specimens : figured, X 109.

Range. Avon Gorge Z 19-Z 37.

Description. The anterior blade bears 11 denticles fused to near their tips. The
denticles are straight and inclined to the posterior at an angle of 80 °. The posterior
blade is straight and only half the height of the anterior blade. It bears up to 12
denticles, which are fused for the greater part of their length, but free at their tips.
The denticles of the posterior blade are free for a greater part of their length than
those of the anterior blade. The denticles of the posterior blade are straight and
inclined to the posterior at an angle of 45°. The aboral edge in lateral view, is
gently arched. The apical denticle is straight, slightly higher than the posterior

178 BRITISH AVONIAN CONODONT FAUNAS

denticle of the anterior blade, and inclined to the posterior at an angle of 70 °. It is
also three times the width of the blade denticles. The small circular basal cavity is
situated beneath the apical denticle. The aboral edge is sharp.

Remarks. Ozarkodina cf. elegans, as interpreted in this study, is characterized by
having longer denticles on the anterior blade than on the posterior blade.

Ozarkodina sp.
Plate 27, figs. 9-11

Material. 93 specimens : figured, X 306, X 307, X 308.

Range. Avon Gorge K 2-S 53.

Remarks. A number of broken specimens which contain part of the anterior, or
posterior blades, have been found, but it is impossible to refer them to any species
with certainty.

Genus PATROGNATHUS gen. nov.

Derivation of name. From the Latin pater — father.

Diagnosis. Symmetrical platform conodonts, with lanceolate platform and
short anterior median blade, generally of five denticles, the most posterior one of
which is higher than the others. The platform bears a row of 6 to 9 nodes on either
margin, separated by a central trough. The basal cavity is large, extending almost
the complete length of the aboral surface of the platform, asymmetrical and laterally
flared. A small posterior blade, composed of two denticles, is developed in a few
specimens, but there is no carina extending along the platform.

Type species. Patrognathus variabilis gen. et. sp. nov.

Description. As for Patrognathus variabilis sp. nov.

Remarks. Patrognathus is similar to the previously described genera Taphro-
gnathus Branson & Mehl, and Streptognathodus Stauffer & Plummer, but has a wider
and more flared basal cavity. Rexroad (1958A) considered Taphrognathus and
Streptognathodus to be homoeomorphs, but Lindstrom (1964 : 173) considered Taphro-
gnathus to be a synonym of Streptognathodus. The present authors believe Rexroad's
interpretation to be correct, and regard Patrognathus as another broad homoeomorph,
which is present at the base of the Tournaisian and possibly in the uppermost Upper
Devonian.

Glenister & Crespin (1959) reported Taphrognathus from the Upper Devonian strata
of the Fitzroy Basin in Australia. The specimens have an anterior blade which is
lateral in position and, therefore, appear referable to our new genus Clydagnathus.
Likewise Conil, Lys & Mauvier (1964) reported, but did not illustrate, Taphrognathus
sp. from the Tni b -Tn2b horizons of the Franco-Belgian Province. If the anterior
blade is lateral in position, then their specimens should be referred to Clydagnathus
gen. nov. Glenister & Klapper (1966, PI. 94, fig. 3) have found specimens of
" Scaphignathus " in Australia identical to our Clydagnathus. In one sample it

BRITISH AVONIAN CONODONT FAUNAS

179

occurs 150 ft. below the first appearance of 5. aculeatus, but in another it occurs
with S. aculeatus and Palmatolepis glabra. Sandberg & Klapper (1967) have also
found the genus Clydagnathus in several sections in Wyoming and Montana, and the
genus Patrognathus in the Windy Gap Formation of Wyoming, where it is associated
with S. sulcatus (see also p. 54)

The Lower Devonian Eognathodus Philip differs from Patrognathus in the form of
the anterior blade, although the genera resemble one another in overall form.

Patrognathus variabilis gen. et sp. nov.
Plate 2, figs. 8a-nc

Derivation of name. From the great variability of this form.

Diagnosis. Elongate, symmetrical form, possessing lanceolate platform and
medial blade. Carina absent. Posterior denticle of blade twice as large as other
blade denticles. Cavity flared, elongate, covering most of platform. Base of
cavity and blade grooved.

Material. 625 specimens : Holotype X 311, Paratypes X 519, X 309, X 310
(all figured).

Type locality and horizon. Avon Gorge, K Zone. Sample KL2.

Range. Avon Gorge Samples K i-K 17, North Crop Samples KL i-KL 12.

Description. The unit is symmetrical, the platform being lanceolate and
straight to slightly curved. The blade varies in length, but is commonly a little

A Orol view

High denticle of blade

Blade

Platform

Posterior

Platform denticle

Position of basal cavity

B. Aboral view

High denticle of blade

Anterior edge
Flared basol cavity

Anterior edge

High denticle of blade
.^Orol edge

Posterior edge

Aboral edge

Position ot basal cavity
C. Lateral view

Fig. 34. Patrognathus sp. showing morphological terms used in the text.

i8o

BRITISH AVONIAN CONODONT FAUNAS

shorter than the platform. It is situated medially and bears from 4 to 8 denticles,
the posterior-most being twice as large as the remainder. There is a general decrease
in size anteriorly, and the denticles are more or less erect. The base of the blade is
grooved.

Each side of the platform bears a marginal row of laterally elongate nodes, which
are transversely paired. These are replaced posteriorly by a single series of medial
transverse ridges, composed of two nodes. An additional node is generally
developed on the left side of the platform (viewed from the posterior). This addi-
tional node, situated at the anterior end of the platform, is developed on the left
margin of the platform, irrespective of whether the unit is laterally curved to the
right or the left. The number of nodes in each row ranges from 4 to 11. The unit is
arched slightly in lateral view and the platform has a nodose edge.

In aboral view the cavity is slightly asymmetrically expanded, the inner half being
shorter and more inflated. The base of the cavity is grooved.

Remarks. Although P. variabilis possesses a variable number of nodes on both
the blade and platform, calculations of denticle density of both blade and platform
and the construction of a scatter diagram of this information, suggest that this vari-
tion is continuous (see Fig. 35). The additional node at the anterior of the inner row
of lateral nodes on " right " specimens appears to be constant and implies that
paired members of P. variabilis were not symmetrical. Other examples of this
asymmetry are to be seen in the genera Cavusgnathus, Scaphignathus, Mestognathus
and Pseudopolygnathus.

SCATTER DIAGRAM TOR DENTICLE DENSITY
OF PATROGNATHUS VARIABLIS.

♦ O CD

-KL2 22 PLOTS
>«KL3 54PLOTS

15 20 30

platform denticle density

blade denticle density • no of blade oenticles
length or blade in mm

platform denticle densityb No of platform denticles
length of platform in mm

Fig. 35. Scatter diagram to show the relationship between the density of denticles on the
blade and those on the platform of the species Patrognathus variabilis.

BRITISH AVONIAN CONODONT FAUNAS 181

Genus PLECTOSPATHODUS Branson & Mehl 1933

1933 Plectospathodus Branson & Mehl : 47.
Type species. Plectospathodus flexuosus Branson & Mehl.

Plectospathodus ? sp. nov. A
Plate 25, figs. 8a-9

Material. 3 specimens : figured, X 312, X 313.
Range. North Crop ZLA 33.

Description. A plectospathodid characterized by a long anterior bar ; denticles
free standing, sub-circular in cross-section and posteriorly inclined ; those in the
median third the largest. Apical denticle larger than bar denticles, ovate in cross-
section, and posteriorly and laterally inclined. Posterior bar about equal in length
to anterior bar, twisted and with slight inward curvature, the posterior tip down-
flexed. Denticles small, fine, except for terminal denticle, which is as large as apical
denticle, and may have small denticles developed on its posterior face.

The basal cavity is open, flared on the inner side, with a " nick " in the inner lip
beneath the apical denticle ; it extends beneath the posterior and anterior bars for a
short distance.

Remarks. The genus Plectospathodus has previously been described only from
rocks of Upper Silurian and Lower Devonian age, but these specimens agree perfectly
with the generic description given by Branson & Mehl (1933 A : 47).

Plectospathodus ? sp. nov. B
Plate 25, figs. 10-12

Material. 4 specimens : figured, X 427, X 428, X 314.

Range. North Crop 3D 14/15-3D 19.

Description. Very small units consisting of two bars, roundly arched at their
junction. Oral edges denticulate. A conspicuous apical denticle. Denticles of

Apical denticle

Terminal denticle

Posterior bar

Fig. 36. Plectospathodus sp. showing morphological terms used in the text.

182 BRITISH AVONIAN CONODONT FAUNAS

variable size, inclined posteriorly ; at or near posterior end of unit a relatively
enormous, greatly elongated denticle, slightly greater in basal width than apical
denticle.

The inner lateral face is generally convex, with a rather flat oral shoulder on which
the denticles are developed. The denticulation of the anterior bar consists of a
series of rather small inconspicuous basally confluent denticles, all inclined equally
posteriorly at an angle of about 45 ° to the oral edge of the bar. The anterior end is
roundly spatulate and there is a very feeble basal flare below the apical denticle.
The apical denticle is biconvex in cross-section, with blunt anterior and posterior
edges, and is curved slightly inward, as well as being inclined posteriorly. On the
posterior bar there is a series of denticles which decrease in size towards the distal
end ; they are basally confluent and have sharp free tips, the most posterior, or the
one next to it, being much the largest. The posterior portion of the posterior bar is
straight-edged, but the posterior aboral corner is bluntly rounded. The whole aboral
surface of the unit is gently concave in lateral view and the unit tends to be bowed
inwards, as well as the main denticles being rather incurved. In outer lateral view
the whole unit is rather flat and is slightly indented below the apical denticle. The
basal surface is flared on the inner lateral face below the apical denticle, and there is a
broad cavity in this position, which rapidly decreases anteriorly and posteriorly, to
be extended along part of both bars as a shallow longitudinal slit.

Genus POLYGNATHUS Hinde 1879
1879 Polygnathus Hinde : 359.
Type species. Polygnathus dubia Hinde 1879.

Polygnathus communis communis Branson & Mehl
Plate 12, figs. 2a-5c

1934 Polygnathus communis Branson & Mehl : 293, PI. 24, figs. 1-4.

1934 Polygnathus communis Branson & Mehl ; E. R. Branson : 308, PI. 25, figs. 5, 6.

1938 Polygnathus communis Branson & Mehl ; Branson & Mehl : 145, PI. 34, figs. 39-41.

1939 Polygnathus communis Branson & Mehl ; Cooper : 399, PI. 39, figs. 1, 2, 9, 10, 23, 24.
1939 Polygnathus adola Cooper : 399, PI. 39, figs. 33-36.

x 939 Polygnathus marginata Branson & Mehl ; Cooper : 401, PI. 41, figs. 15, 16.

1944 Polygnathus communis Branson & Mehl ; Branson & Mehl in Shimer & Schrock : 245,

PI. 94, figs. 29-31.
1944 Polygnathus communis Branson & Mehl ; E. B. Branson : 208, 221, PI. 39, figs. 39-41.
1947 Polygnathus communis Branson & Mehl ; Mehl & Thomas : 15, PI. 1, fig. 36.
1949 Polygnathus communis Branson & Mehl ; Youngquist & Patterson : 62, PI. 15, figs.

7.8.
1949 Polygnathus communis Branson & Mehl ; Thomas : 411, PI. 3, fig. 70.
1951 Polygnathus communis Branson & Mehl ; Youngquist & Downs : 787, PI. in, figs.

4, 5, 19, 20.
1951 Polygnathus communis Branson & Mehl ; Hass : 2538, 2539, PI. 1, fig. 10.
1956 Polygnathus communis Branson & Mehl ; Bichoff & Ziegler : 156, PI. 12, figs. 1-3.
1956 Polygnathus communis Branson & Mehl ; Hass : 24, 25, PI. 2, figs. 3-5.

BRITISH AVONIAN CONODONT FAUNAS 183

1957 Polygnathus communis Branson & Mehl ; Bischoff : 42, PI. 2, figs. 23-27.

1957 Polygnathus communis Branson & Mehl ; Ziegler in Fliigel & Ziegler : 46, PI. 2,

fig- 15-
!959 Polygnathus communis Branson & Mehl ; Hass : 390, PI. 49, figs. 9-11, 13.
1959 Polygnathus communis Branson & Mehl ; Helms : PI. 3, fig. 11.
J 959 Polygnathus communis Branson & Mehl ; Voges : 288, PI. 34, figs. 1-7.
i960 Polygnathus communis Branson & Mehl ; Ziegler : PI. 1, fig. 9.
i960 Polygnathus communis Branson & Mehl ; Dvorak & Freyer : 884-888, PI. 1, figs. 15,

16.
i960 Polygnathus decorosa Stauffer ; Dvorak & Freyer : 882, PI. 2, figs. 1-2.
1961 Polygnathus communis Branson & Mehl ; Beach : 49, PI. 6, figs. 1-4.
1961 Polygnathus communis Branson & Mehl ; Scott & Collinson : 130, PI. 1, figs. 6-10

PI. 2, fig. 30.

1961 Polygnathus communis Branson & Mehl ; Freyer : 70.

1962 Polygnathus pura Voges; Miiller : 1388, text-fig. 2a, b.

1964 Polygnathus communis communis Branson & Mehl ; Rexroad & Scott : 33, PI. 2,

figs. 17, 18.
1964 Polygnathus communis Branson & Mehl ; Higgins, Wagner-Gentis & Wagner : 225,

PI. 5, fig. 30.

1964 Polygnathus communis Branson & Mehl ; Budurov & Tschurner : PI. V, figs, ia, b,
2a, b, 12, 18.

1965 Polygnathus communis Branson & Mehl ; Spasov : 95, PI. 2, figs. 15, 15a.
1965? Polygnathus communis Ethington : 581, PI. 67, fig. 7.

Material. 740 specimens : figured, X 346, X 347, X 348.
Range. North Crop KL 3-ZL 10, Avon Gorge K 3-C 9.

Description. The platform varies in shape from ovate to lanceolate, but is
unornamented except for a medial nodose carina. The platform edges tend to be
upturned and thickened. The anterior blade varies in length but is commonly equal
to the platform length, bearing from 10 to 16 laterally compressed, fused denticles ;
the oral outline of the blade is convex.

In aboral view the cavity is fairly large, circular, and situated at the junction of the
platform and the anterior blade. In some specimens the cavity appears on the blade.
The aboral surface of the unit posterior to the cavity tends to be concave. The
cavity is extended as a tapering slit along the anterior blade, to a point just anterior
to its mid point. A keel runs from the margin of the main cavity to the posterior tip
of the platform ; its aboral surface may bear a fine groove. The aboral surface
makes a sharp obtuse angle with the lateral faces of the outer platform margins,
giving a chine-like aboral appearance to the unit.

Remarks. Carinate and bifurcate subspecies of Polygnathus communis known
from America are not present in our fauna, but the species is very variable throughout
the section. A single specimen (PI. 12, ia-c) is obviously close to individual speci-
mens assigned to this species, but differs in the general form of the oral surface of the
platform. The anterior lateral margins of the platform are strongly constricted and
upturned, giving almost a Siphonodella-like appearance to the anterior portion. The
posterior portion is wide, shallow and bluntly rounded posteriorly, the whole having
the general appearance of a shallow spoon. There is no ornamentation and the
carina continues as a series of distinct blunted nodes to the posterior end of the

184

BRITISH AVONIAN CONODONT FAUNAS

platform, the most posterior node being the smallest of the six exposed on the
broken specimen.

Polygnathus bischoffi sp. nov.
Plate 13, figs. 8a-nc

1957 Polygnathus inornata E. R. Branson ; Bischoff : 42, PI. 2, figs. 17, 18, 20, 21.
1959 Polygnathus cf. flabella Branson & Mehl ; Voges (partim) : PI. 34, fig. 11 only.
1964 Polygnathus inornata E. R. Branson ; Higgins : 225, fig. 4, PI. V, fig. 29.

Derivation of name. After Dr. G. Bischoff.

Diagnosis. Arrow-shaped platform ; widest in anterior half, tapering to pointed
posterior. Unit usually slightly arched in lateral view. Platform ornamented by
delicate ribs, confined to margin. Platform margin upturned in anterior half. Small
basal cavity, circular in outline, with thickened lips, situated anteriorly.

Material. 64 specimens : Holotype X 349, Paratypes X 350, X 351, Hypotype
X 352 (all figured).

Type locality and horizon. South Wales Coalfield. Sample SCC, C Zone, Fall
Bay, Gower.

Range. Avon Gorge C 11-C 24.

Description. The platform is arrow-shaped, with a straight to slightly curved
axis. In lateral view the unit is arched. The platform is widest anteriorly, and at

Anterior blade
ANTERIOR

Oral surface

Platform

POSTERIOR

LATERAL VIEW

Carina

Platform

Cavity

Cnine

ORAL VIEW

ABORAL VIEW

Fig. 37. Polygnathus sp. showing morphological terms used in the text.

BRITISH AVONIAN CONODONT FAUNAS 185

mid-length it is only slightly narrower than at the anterior. The platform is two and
a half times as long as wide and tapers to the pointed posterior. The margins of the
platform are slightly upturned in the anterior and mid-thirds, and the oral surface is
ornamented by a number of transverse ridges, which are more strongly developed at
the margin. The margins of the platform are equal in height to the carina and on
either side of the carina there is a trough, which is more strongly developed at the
anterior. The trough opens to the anterior. The anterior blade is of the same length
as the platform and consists of 6 denticles, which are highest at mid-length. The
carina consists of nodes fused for their entire length and extends a short distance
beyond the posterior extremity of the platform. The basal cavity; situated in the
anterior third of the aboral surface, is small and rounded in outline, with thick lips.
In some specimens a groove extends posteriorly from the basal cavity to the posterior
extremity of the unit.

Remarks. Compared with Polygnathus inornatus inornatus the platform of P.
bischoffi is more elongate, broader in the anterior half and tapering uniformly in the
posterior half. The platform also has more convex margins and is arched in lateral
view. Polygnathus bischoffi has less strongly developed anterior troughs than
Polygnathus inornatus inornatus, because the margins of the platform in the anterior
third are not as strongly upturned.

Polygnathus bischoffi is characteristic of the C Zone both in the Bristol area and in
other parts of the South West Province. It makes its first appearance near the base
of the Laminosa Dolomites. Bischoff obtained the specimens of Polygnathus
inornatus which he illustrated from the Cu II Siphonodella Subzone. A specimen,
which Voges referred to as Polygnathus cf. flabellus, and which is here placed in
synonomy, was found by him in the Siphonodella p. triangulus triangulus Zone,
which is Upper Cu I in age.

The " Polygnathus inornata " group

Rexroad & Scott (1964 : 35) remarked that " P. inornata is a remarkably varied
species ". They included within their concept of this species P. Sagittarius Young-
quist & Patterson, a junior synonym of P. lacinatus Huddle which we regard as a
separate and variable species in its own right. However, even within the much
narrower terms of our present diagnosis, there is still a marked degree of variability.

The transition between P. inornatus and P. lobatus was noted by Rexroad & Scott
(1964 : 35), and can also be seen in our faunas. There is also a tendency for the
development of a rostral ridge in both P. inornatus and P. lobatus. In a few cases,
breakdown of the transverse platform ridges into transverse lines of nodes is also
seen. The P. inornatus fauna occurs within the range of the genus Siphonodella and
these morphological details are characteristic of that genus, which is extremely rare
(°'5% °f total conodont fauna) in our faunus. It seems that the P. inornatus group
show morphological developments which carry it towards, but not as far as, the
characteristic morphology of the genus Siphonodella.

The P. inornatus s.s. forms with a well-developed rostral ridge are here given sub-

iSo

BRITISH AVONIAN CONODONT FAUNAS

specific rank as P. inomatus rostratus and the P. lobatus forms with the same feature
are referred to P. lobatus inflexus.

Polygnathus inomatus inomatus Branson & Mehl
Plate 10, figs. 4a-6c

1934

1938

non 1939

1944
1949

1949
1951

non 1956

1956

non 1957

1957
non 1958

1959

non 1964

1964

Polygnathus inornata Branson & Mehl :
Polygnathus inornata Branson & Mehl ;
Polygnathus inornata Branson & Mehl ;
Polygnathus inornata Branson & Mehl ;
gnathus inornata rostrata).
Polygnathus inornata Branson & Mehl ;
Polygnathus inornata Branson & Mehl
figs. 4l 5, 9, 13.

Polygnathus inornata Branson & Mehl ;
Polygnathus inornata Branson & Mehl ;

293, PI. 24, figs. 5-7.
E. R. Branson : 309, PI. 25, figs. 8, 26.
Branson & Mehl : 132, 146, PI. 34, fig. 37.
Cooper : 400, PI. 39, figs. 11, 12 (—Poly-

E. B. Branson : PI. 39, fig. 37.

; Youngquist & Patterson : 64, PI. 17,

Thomas : 409, 411, PI. 3, fig. 36.
Youngquist & Downs : 787, 788, PI. 111,

figs. 17, 18 (non PI. in, fig. n=P. lobata lobata).

Polygnathus inornata Branson & Mehl ;
(=P.flabella).

Polygnathus inornata Branson & Mehl ;
Polygnathus inornata Branson & Mehl
(=P. lacinata lacinata).
Polygnathus inornata Branson & Mehl
fig. 7 (=P. nodomarginata) .
Polygnathus inornata Branson & Mehl ;
Polygnathus inornata Branson & Mehl ;
Polygnathus inornata Branson & Mehl ;
figs. 17-20 = P. lacinata lacinata).
Polygnathus inornata Branson & Mehl ;
PI. 5, fig. 29 (=P. lacinata lacinata).
Polygnathus inornata Branson & Mehl ;

Bischoff & Ziegler : 157, PI. 12, figs. 4, 5

Hass : 25, PI. 2, figs. 14, 15.
Bischoff : 42, PL 2, figs. 17,

20, 21

; Ziegler in Fliigel & Ziegler : 46, PI. 2,

Cloud, Barnes & Hass : PI. 5, fig. 6.
Klapper : 1089, PI. 142, figs. 2, 3.
Voges : 291, PI. 34, figs. 12-16, (non PI. 34,

Higgins, Wagner-Gentis & Wagner : 225,

Rexroad & Scott 35, PI. 2, figs. 19, 20.

Material. 82 specimens : figured, X 353, X 354, X 355.
Range. North Crop KL 16-KL 20.

Description. The platform is semi-circular in cross-section and is ornamented
by transverse ribs, which terminate on the platform edge as low nodes. The ridges
may break up into transverse rows of nodes. The platform is fairly flat at the
posterior, but anteriorly it has deep troughs, separated by a nodose carina. The
whole unit is nearly symmetrical.

The carina is a continuation of the free blade, and runs the whole length of the
platform, terminating at the posterior end in a point. The blade is thin and highest
in its mid-part, the aboral outline being straight.

Aborally the unit is keeled, the basal cavity occurring as a small pit at, or just
posterior to, the junction of the anterior blade and the platform. The cavity edges
tend to be thickened.

Remarks. Our specimens agree closely with those of Rexroad & Scott (1964).

BRITISH AVONIAN CONODONT FAUNAS 187

Polygnathus inornatus rostratus subsp. nov.

Plate 10, figs. ja.-gc

? 1939 Polygnathus irregularis Cooper : 400, PI. 39, figs. 57, 58.
1962 Pseudopolygnathus ? cf. Pseudopolygnathus triangula Voges ; Miiller : 1388, text-figs,
ga-c.

Derivation of name. From the development of a rostral ridge on the inner
platform.

Diagnosis. P. inornatus possessing rostral or pseudorostral ridge on inner
platform.

Material. 28 specimens : Holotype X 530, Paratypes X 356, X 357 (all
figured).

Type locality and horizon. North Crop. Sample KL 4.

Range. North Crop KL 4-KL 16-KL 20, ZL i, Avon Gorge K 12-K 14.

Description. Specimens of P. inornatus rostratus agree closely with specimens
of P. inornatus s.s., apart from the configuration of the inner margin. There is a
tendency for the anterior part of the inner margin to move towards the anterior
blade, the posterior part then becoming lobate. The anterior inner margin tends to
run towards the carina for a very short distance in more advanced forms.

In some cases there tends to be a thickening of the aboral portion of the platform
wall, so that in oral view the platform edge does not form the inner edge of the unit.

Remarks. This subspecies includes all specimens showing a breakdown in the
smoothness of the inner edge. Thus in more advanced forms a pseudo-rostral ridge
can be seen (e.g. PI. 10, fig. 7b). In less advanced forms there may be thickening of
the aboral edge and a breakdown of the curvature of the inner edge (e.g. PI. 10,
fig. 9b). The strength of development of the ridge bears some relationship to both
ontogeny and to stratigraphic position. This involves an offset, tilt and deflection
towards the carina of the inner lateral margin, the pseudo-rostral ridge having a
sharp and well-defined outer face. The posterior portion of the ridge, which runs
sub-parallel to the carina, is conspicuously higher than the adjacent inner margin,
although the posterior termination is low and indistinct.

Polygnathus inornatus vexatus subsp. nov.
Plate 10, figs. ia-3c

Derivation of name. From the troublesome problem of specific assignment.

Diagnosis. Subspecies of P. inornatus. An arched unit with symmetrical
platform, curved axis, and fairly long blade, composed of broad, fused, chevron-
tipped denticles. Carina low, nodose, extending beyond platform as short posterior
blade. Symmetrical lanceolate platform, ornamented with medium to strong
transverse ribs ; platform edges serrated. Basal cavity small, occurring near
junction of blade and platform.

Material. 5 specimens : Holotype X 358, Paratypes X 359, X551 (all figured) .

[88 BRITISH AVONIAN CONODONT FAUNAS

Type locality and horizon. North Crop. Sample KL 19.

Range. North Crop KL 17-KL 19, Avon Gorge K 17.

Remarks. As was noted by Rexroad & Scott (1964) P. longiposticus belongs to
the P. inornatus group of polygnathids. It can be distinguished from P. inornatus
s.s., by the lanceolate platform and the longer free blade. The present subspecies
approaches P. longiposticus in these respects.

Polygnathus lacinatus Huddle

Certain polygnathids with a lanceolate platform and an elongate, excavated cavity
were referred to a new species, P. lacinatus, by Huddle (1934). This species was
recognized by Cooper (1939), but Youngquist with various co-authors (Youngquist &
Patterson 1949, Youngquist, Miller & Downs 1950, and Youngquist & Downs 1951),
referred similar forms to P. Sagittarius Youngquist & Patterson. German workers,
describing collections from condensed sequences of strata, included P. lacinatus
within the species P. inornatus E. R. Branson, thus extending both the stratigraphic
range and concept of that species. The distinctive feature of P. lacinatus is the
marked longitudinal extension of the rim of the basal cavity, which is often half the
total platform length (e.g. PI. 11, fig. 9b).

P. lacinatus appears to us to be a valid species. It is restricted to an interval
comparable with beds of Cu II fi/y age in Europe. Its generic affinities are somewhat
doubtful. Huddle stated that the platform was a perfect polygnathid platform,
although the basal cavity differs markedly from the " typical " cavity of that genus.
The possession of a large basal cavity brings it within the morphological scope of the
genus Pseudopolygnathus, but the lack of asymmetry of the cavity and the poly-
gnathid nature of the platform lead us to conclude, like Huddle, that this form is a
polygnathid. Later phylogenetic work may show that this is not the case. Within
our faunas there appear to be several variants, and these have been referred to new
subspecies. Forms referred to P. lacinatus lobatus show lobation of the posterior
part of the outer platform, and considerable narrowing of the anterior part of the
platform, with upturning of the platform edges. This tends to give these specimens
an overall siphonodellid appearance, but the basal cavity and lack of rostral ridges
set them apart from the genus Siphonodella.

Polygnathus lacinatus asymmetricus subsp. nov.
Plate 11, figs. ia-4c

Derivation of name. From the asymmetrical development of the platform.

Diagnosis. Subspecies of P. lacinatus with reduced inner platform, giving
asymmetrical platform outline.

Material. 295 specimens : Holotype X 361, Paratypes X 360, X 362, X 363
(all figured).

Type locality and horizon. North Crop. Sample ZLA 32.

BRITISH AVONIAN CONODONT FAUNAS 189

Range. North Crop ZLA 29-ZLA 33. Avon Gorge Z 33-C 20.

Description. The anterior blade and the anterior portion of the platform are
exactly comparable with P. lacinatus s.s., but the posterior part of the inner platform
is reduced and does not extend to the posterior termination, the carina being
extended posteriorly as a short posterior free blade.

Polygnathus lacinatus circaperipherus subsp. nov.
Plate ii, figs. I2a-i5c

Derivation of name. From the platform edge, which encircles the posterior
portion of the platform.

Diagnosis. P. lacinatus with platform margin complete around posterior part of
platform ; posterior section of carina obsolescent.

Material. 32 specimens : Holotype X 364, Paratypes X 365, X 366, X 367
(all figured).

Type locality and horizon. North Crop. Sample ZLA 32.

Range. North Crop ZLA 17-ZLA 30, Avon Gorge C 7.

Description. This subspecies is very similar to P. lacinatus except for the
posterior platform termination. The platform edge is wrapped around the posterior,
the carina dying away before it reaches the posterior. In aboral view the keel is also
terminated abruptly and the whole posterior of the unit is rounded off. The
posterior outline may be expanded and club-like (e.g. PI. 11, fig. 12b) to bluntly
pointed (e.g. PI. 11, fig. 15a). There is some variation in the form of the basal
cavity. In some specimens it is extended relatively further posteriorly than in
others. In neither case, however, is there an ungrooved posterior keel developed
behind it.

Remarks. This morphological variation is also seen in our faunas in the species
of P. communis.

Polygnathus lacinatus lacinatus Huddle
Plate 11, figs. 8a-ioc

1934 Polygnathus lacinata Huddle : 95, PI. 8, figs. 1-3.

J 939 Polygnathus lacinata Huddle ; Cooper : 401, PI. 40, figs. 3, 4.

1949 Polygnathus sagittaria Youngquist & Patterson : 66, PI. 15, figs. 9, 10.

1950 Polygnathus aff. Polygnathus sagittaria Youngquist & Patterson ; Youngquist, Miller &
Downs : 527, PI. 67, figs. 2-4.

1951 Polygnathus sagittaria Youngquist & Patterson ; Youngquist & Downs : 788, PI. 111,
figs. 7-9-

1959 Polygnathus inornata E. R. Branson ; Voges : 291, PI. 34, figs. 17-20 (non PI. 34,
figs. 12-16 = P. inornata).

Material. 753 specimens : figured, X 368, X 369, X 370.
Range. North Crop ZLA 29-ZL 19, Avon Gorge Z 32-C 20.

igo BRITISH AVONIAN CONODONT FAUNAS

Description. The platform is lanceolate, from two to three times as long as wide,
being widest at mid-point, narrowing considerably both to the anterior and to the
posterior. The platform ornament consists of a fairly strong carina, often extended
beyond the platform as a short posterior blade, the nodes being slightly higher in this
region. There is an unornamented trough on either side of the carina, accentuated by
the upturning of the platform edges, especially in the anterior. The upturned
platform edges bear short transverse ridges, terminating in denticles, which give a
crenulate platform edge. The ornament varies considerably ; the juveniles tend
to be smooth, and the strength of the ridges varies in the adults. The anterior
blade is fairly long and high, consisting of 7 to 8 tall, laterally compressed, fused
denticles, which are highest at the anterior end and decrease regularly in height
towards the junction with the platform.

In aboral view the unit is very distinctive, the basal cavity being large and
elongate. It tends to close slightly with age, but is always extremely large, being
widest at the anterior, and narrowing gradually towards the posterior, where a short
grooved keel is present.

Remarks. This subspecies is distinguished by the large basal cavity. Forms
described as P. marginatus Branson & Mehl, by Rexroad & Scott (1964 : 37) are
recorded as having large basal cavities and may be referable to P. lacinatus s.s., but
the lack of an aboral illustration makes us hesitate to include them in the present
synonomy. Orally this subspecies is highly variable, and some forms might be
mistaken for P. inornatus. The most distinctive feature is, however, the form of the
basal cavity. In this, apart from the length of the basal cavity proper, the most
conspicuous feature is the very strong lateral and longitudinal extension of the lips
around the cavity. These extend posteriorly to the cavity, and become obsolescent
only in the posterior quarter of the unit, although they narrow posteriorly towards
that point from their maximum at the posterior termination of the cavity. There is
no chine-like structure on the aboral surface, and the low-angle sloping outer aboral
margins of the platform join the lateral lips of the cavity at a sharp angle. Most
specimens tend to show an almost siphonodellid development of the anterior end of
the platform, though this itself shows some variation. The Siphonodella-like spout
of P. lacinatus prelobatus is even more strongly developed than that of the present
subspecies. The strongly developed posterior aboral extension of the carina, and
the deep anterior blade give a distinctive appearance to the platform in lateral view.
It tends to " ride high " on the surface of the lateral blade.

Polygnathus lacinatus prelobatus subsp. nov.
Plate 11, figs. 5a-7b, na-c

Derivation of name. From the lobate nature of the inner platform.

Diagnosis. Subspecies of P. lacinatus with lobate postero-inner platform.

Material. 179 specimens : Holotype X 371, Paratypes X 372, X 373, X 374
(all figured).

BRITISH AVONIAN CONODONT FAUNAS 191

Type locality and horizon. North Crop. Sample ZLA 32.

Range. North Crop ZLA 29-ZLA 33, Avon Gorge Z 33-C 9.

Description. The free blade and outer platform are closely similar to P. lacinatus
s.s., but there is modification of the inner posterior platform margin. The postero-
inner portion tends to be produced as a lobe, narrowing rapidly to the posterior
termination, which is formed by a posterior projection of the carina, to give a short
posterior anterior blade. The anterior inner platform tends to be considerably
upturned and the platform edge is very close to the anterior blade. In aboral view
the unit exhibits the characteristics of P. lacinatus s.s.

Remarks. The narrowing of the anterior portion of the platform and the lobation
of the posterior inner platform give this subspecies the aspect of Siphonodella, but the
basal cavity precludes the inclusion of these forms in this genus.

Polygnathus lobatus lobatus Branson & Mehl
Plate 9, figs. 5a-8c

1938 Polygnathus lobata Branson & Mehl : 146, PI. 34, figs. 44-47.

1939 Polygnathus lobata Branson & Mehl ; Cooper : 401, PI. 39, figs. 29, 30.
J 939 Polygnathus curta Cooper (partim) : 400, PI. 39, figs. 37, 38 only.
1949 Polygnathus lobata Branson & Mehl ; Thomas : 411, 418, PI. 3, fig. 11.
1949 Polygnathus cunulae Youngquist & Patterson : 62, PI. 15, figs. 11-15.

195 1 Polygnathus inornata Branson & Mehl ; Youngquist & Downs : 787, PI. in, fig. 11

(non PI. in, figs. 17, 18 = P. inornata inornata).
1957 Polygnathus lobata Branson & Mehl ; Bischoff : 42, PI. 2, fig. 19.
1964 Polygnathus lobata Branson & Mehl ; Rexroad & Scott : 35, PI. 2, figs. 15, 16.

Material. 21 specimens : figured, X 376, X 377, X 378, X 440.
Range. North Crop KL 16-KL 20.

Description. This unit is boat-shaped, with a curved axis. The platform is flat
in the posterior portion but deepens to form two troughs either side of the carina in
the anterior portion. The unit tends to be symmetrical in the anterior half, but in
the posterior, the outer platform wall flares out to give a lobate process. The plat-
form then narrows rapidly to give a pointed posterior termination. The ornament
consists of transverse ridges dying out towards the carina and terminating on the
platform edges as low nodes or short chevron-shaped denticles. The carina is
sinuous, consisting of low nodes which merge with the free blade, which is itself short
and high, being highest at its mid point.

In aboral view the unit is keeled, there being a small cavity posterior to the junc-
tion of the free blade with the platform. The antero-lateral corners project as two
" horns " in aboral view. The whole central part of the aboral surface tends to be
more or less flat and unornamented, except for the sinuous median ridge. The outer
margin of this flattened chine-like area is sharp, and the flat sloping faces of the outer
aboral edges join it at a sharp angle. The surface of the chine is finely striate, with
the striations more or less parallel to the outer margins. In at least some specimens

(92 BRITISH AVONIAN CONODONT FAUNAS

(e.g. PI. 9, fig. 6a-c, X 376), the aboral cavity is situated about a quarter of the total
length of the platform from the anterior end.

Remarks. This form is distinguished from P. inomatus s.s. by possessing a lobe
on the outer margin. The two subspecies appear to be transitional.

Polygnathus lobatus inflexus subsp. now
Plate 9, figs. 9a-c

Derivation of name. From the inflexing of the inner platform margin.

Diagnosis. P. lobatus in which inner anterior lateral margin is more or less
strongly inflexed.

Material. 4 specimens : Holotype X 375 (figured).

Type locality and horizon. North Crop. Sample KLM 1.

Range. North Crop KL 16-KL 20, Avon Gorge K 12.

Description. In a few specimens whose general characteristics are similar to P.
lobatus lobatus, there is a marked tendency for the inflexing and upraising of the inner
anterior lateral margin of the platform. This tends to be confined to the anterior
third or half of the platform. The oral edge bears a series of irregular, low, rounded,
confluent denticles, giving a bluntly serrate margin. It stands conspicuously higher
than the carina and rather higher than the opposing outer lateral margin. It reaches
almost the height of the large denticles in the median portion of the anterior blade,
and it runs broadly sub-parallel to the line of the anterior portion of the carina. It is
at the posterior end of this inflexed portion that the carina tends to be more or less
strongly laterally deflected.

Remarks. This form appears to be undergoing similar adaptations to those of
P. inomatus rostratus within the species P. inomatus. This may imply either close
relationships between P. lobatus and P. inomatus or independent (functional?)
convergence.

Polygnathus sp.
Plate 15, figs. 9a-c

Material, i specimen : figured, X 531.

Range. Farlow Sample FAR 4A.

Description. This specimen seems to be a pathological individual of the genus
Polygnathus. It is distinguished by a lip-like secondary development on the inner
lateral platform, so that although the anterior edge of the platform forms a typical,
open, spout-like development on the inner lateral side and the inner anterior lateral
margin, it is strongly developed and upturned. It ceases after running for about a
quarter of the total length of the platform, and the platform itself is then bent
outwards, as though some injury had taken place to the individual and then been
reformed. The rather low sinuous margin of the platform gives a wide platform for

BRITISH AVONIAN CONODONT FAUNAS 193

the middle half, but the whole platform is sharply tapered and is pointed posteriorly.
There is a conspicuous lack of general ornament, except for barely perceptible
transverse ridges and nodes on the outer lateral faces, and a median carina, which is
also very inconspicuous, consisting of low fused nodes, which runs posteriorly from
the anterior blade but does not divide the platform into two equal halves. It runs
into the posterior portion of the platform. The anterior inner edge is higher than
any other part of the platform except the median outer lateral edge, and is
ornamented by low fused nodes, up to six in number.

In inner lateral view the " injury " to the inner lateral platform makes a prominent
feature. The platform is deepest anteriorly and the " injury " shows a secondary
projection.

In aboral view the individual shows a typical polygnathid form, with a minute and
thickly-lipped cavity restricted to the anterior fifth of the platform, and extended
anteriorly and posteriorly as a slit-like groove. The anterior blade is poorly
preserved but it is relatively short, with a rounded anterior aboral margin, and has at
least one conspicuous denticle near its posterior end.

Polygnathus sp.

Plate 31, fig. 21

Material. 3 specimens : figured, X 130.

Range. Avon Gorge D 22.

Description. Rexroad (1957 : 41) has noted the presence of small numbers of
polygnathids in the Renault Formation at two localities. He has described three
fragments, and very small numbers of specimens are also present in the D Zone of the
Avon Gorge and the North Crop. In all three cases this represents an abnormally
high stratigraphic occurrence of the genus. In the Mississippi Valley, for example,
its generally accepted range extends upwards only into the Burlington Formation.
A single specimen is illustrated. The anterior blade is broken, but this specimen
displays strongly developed aboral lips with a conspicuous pit developed near the
anterior end of the platform, and a well-developed slit-like basal cavity extending the
whole length of the platform.

Genus PRIONIODINA Ulrich & Bassler 1926

1925 Prioniodina Bassler : 219 (nom. nud.).

1926 Prioniodina Ulrich & Bassler : 17, 18.
1934 Subbryantodus Branson & Mehl : 285.

Type species. Prioniodina subcurvata Ulrich & Bassler 1926.

In 1925 Bassler erected the generic name Prioniodina, and in 1926 with Ulrich as
senior author, he gave the following description : " Base of tooth more or less
curved, crowned with numerous, sub-parallel, rounded, discrete denticles all inclined
in one direction, one of which located in the median third, is considerably larger than
the others. "

194

BRITISH AVONIAN CONODONT FAUNAS

Later, Branson & Mehl (1934A) erected the genus Subbryantodus for " arched
denticulate bars . . . with one or both limbs laterally flexed . . . denticles . . .
laterally compressed . . . closely crowded . . . one denticle of exceptional size,
the apical denticle at the apex of the arch . . . the aboral edge of the bar excavated
beneath the arch apex by a long pit that tends to extend as a distinct groove along
the edge of each limb ".

Branson & Mehl suggested (p. 285) that Stibbryantodus differed essentially from
Prioniodina in the fused, laterally compressed denticles and tendency toward a split
aboral edge. We consider that these differences are not of generic significance and
regard Subbryantodus as a junior subjective synonym of Prioniodina Bassler 1925.

Prioniodina eireica (Collinson & Druce)

Plate 28, fig. 13

Subbryantodus eireica Collinson & Druce (in press).

Material, i specimen : figured, X 315.

Range. North Crop 3D 17.

Description. The distinctive features of this species are the minutely denticu-
lated and very short depressed anterior bar, the massive, recurved, wide, pointed
apical denticle, and the short straight feebly denticulated posterior bar. Below the

Apical denticle

Blade denticles

Posterior_
bar

Anterior bar

Basal cavity

Fig. 38. Prioniodina sp. showing morphological terms used in the text.

BRITISH AVONIAN CONODONT FAUNAS 195

posterior edge of the apical denticle there is a strongly flared basal cavity which,
although laterally wide, is not very deep.

The whole unit is rather small and short and the apical denticle looks altogether
too large for the general proportions of the anterior and posterior bars. The
anterior bar is short, strongly recurved and slender in general construction, making
an angle of about 130 ° with the straight basal margin of the posterior bar in outer
lateral view. The anterior bar bears 2 or 3 small denticles with blunt free tips, but
otherwise basally confluent. They have a tendency to increase in size posteriorly
and stand more or less erect, or only gently posteriorly inclined, to the anterior bar.
The anterior bar is of more or less uniform depth throughout its length, though it
may be a little shallower anteriorly.

The apical denticle is strongly recurved on its anterior edge, but its posterior edge
is straight or only feebly curved. It is sharply pointed and very broad at its base,
being about five or six times as wide as the largest adjacent denticles. It has sharp
anterior and posterior edges and gently convex lateral faces. The posterior bar is
short and minutely denticulate, the denticles being so closely crowded that they are
virtually confluent, except for their blunted tips. The bar decreases in depth
posteriorly and is slightly longer, though shallower than, the anterior bar.

The other conspicuous feature of the unit in outer lateral view is the widely flaring
basal cavity, which forms a conspicuous feature below the posterior half of the apical
denticle. It is less conspicuous in inner lateral view and the whole unit is slightly
bowed inward, having flatter faces.

In aboral view the basal cavity is seen to be asymmetrical, being more widely
flared on the outer lateral face than it is on the inner. On the inner lateral face,
although there is less curvature, the convexity continues towards the tip of the
posterior bar. The whole posterior bar, as well as the posterior half of the apical
denticle, is excavated by the cavity, which is deepest below the posterior edge of the
apical denticle. It is continued anteriorly as a minute slit.

Remarks. Collinson and Druce have discussed the relationship of this species to
similar species of the genus Ozarkodina.

Prioniodina laevipostica (Rexroad & Collinson)

Plate 28, figs. n-i2b

1963 Ozarkodina laevipostica Rexroad & Collinson : 19, PI. 1, figs. 1-6.

Material. 31 specimens : figured, X 316, X 317.

Range. North Crop ZLA 6-ZLA 12, CYD 6-CYD 7.

Description. This species closely approaches P. eireica, but differs from it in the
relatively stronger development of the anterior and posterior bars, the less massive
apical denticle, and the rather less conspicuous basal cavity. Rexroad & Collinson
(1963) noted that their species had a posterior bar which was only partly denticulate,
but both their illustrations and the present specimens show that, in at least some
individuals, the posterior bar is denticulate for most or all of its length. The present

ig6 BRITISH AVONIAN CONODONT FAUNAS

individuals bear up to five closely set, but apically discrete, more or less sharply
pointed denticles, which decrease in size posteriorly and which are inclined at about
45 to the aboral surface of the posterior bar. The posterior bar is deep in its
anterior portion but tapers rapidly towards its posterior end. Its aboral margin is
more or less straight.

The apical denticle is two to three times the width of the largest adjacent denticles
and is sharply to bluntly pointed. There is considerable variation in the form of the
distal end of the apical denticle (see Rexroad & Collinson 1963). Although the
cavity is similar in general form, it is rather shallower and somewhat less asymmetrical
than that of P. eireica, and its anterior extension is also rather more conspicuous.
The edges of both the cavity and the slits along the anterior and posterior bars are
also prominent.

Remarks. Our specimens from the D Zone closely resemble those of Rexroad &
Collinson in overall morphology and in the aboral configuration, but they differ in
denticulation, our specimens having fewer denticles on the anterior bar and more on
the posterior bar. However, Rexroad & Collinson mention that some of their
specimens fall within the limits of our specimens. The variable dentition is thus
due to variation within the species.

Prioniodina latericrescens (Branson & Mehl)
Plate 24, fig. 19
1934 Lonchodina latericrescens Branson & Mehl : 212, PI. 14, fig. 20.

Material. 12 specimens : figured, X 429.

Range. North Crop KL i-ZLA 4.

Description. The unit is bowed and arched, being laterally compressed in
juveniles, but the bars becoming circular in cross-section in adults. The posterior
and anterior bars are of equal length, bearing about 4 isolated, sub-circular,
posteriorly inclined denticles. In aboral view the pit is fairly large and occurs
beneath the apical denticle.

Prioniodina oweni sp. nov.
Plate 28, figs. 5a-c

Derivation of name. After Mr. T. R. Owen.

Diagnosis. Prioniodinid with greatly expanded basal cavity and restricted
posterior bar.

Material. 13 specimens : Holotype X 330 (figured).

Type locality and horizon. R. Clydach, Nr. Gilwern, Lower Z Zone. Sample
ZLA5.

BRITISH AVONIAN CONODONT FAUNAS 197

Range. North Crop ZLA 3-ZLA 27.

Description. The anterior bar is short, bearing about 5 discrete, sub-circular,
posteriorly inclined denticles, whose height increases posteriorly, culminating in the
apical denticle, which is the largest. The posterior bar is very restricted, commonly
bearing 1 or 2 small, discrete, sub-circular, posteriorly inclined denticles.

In aboral view the whole unit is excavated, the basal cavity being expanded and
pear-shaped at the posterior end. The widest part occurs beneath the apical denticle
and it narrows gradually beneath the anterior bar, and rapidly beneath the posterior
bar. The posterior termination tends to be rather blunt. The cavity lips in the
posterior part are thickened to give a small flange.

Remarks. The large basal cavity with excavated bars, together with the short
posterior bar, precludes the placing of this species within the genus Ozarkodina, and
serve to distinguish it from all other prioniodinids.

Prioniodina prelaevipostica sp. nov.
Plate 24, figs. 1-6

Derivation of name. Ancestral form of Prioniodina laevipostica (Rexroad &
Collinson) .

Diagnosis. Short Prioniodina, with large apical denticle and deflected anterior
bar.

Material. 9 specimens : Holotype X 334, Paratypes X 333, X 331, X 332,
X 335. X 336 (all figured).

Type locality and horizon. R. Clydach, Nr. Gilwern, uppermost Z Zone.
Sample ZLA 33.

Range. North Crop ZLA 32-ZL 19.

Description. The whole unit is arched, being surmounted by a tall, laterally
compressed, free standing, posteriorly inclined apical denticle. The anterior bar is
short, depressed through 45 ° and slightly deflected, bearing 2 or 3 tall isolated
denticles, the most anterior ones being very small and posteriorly inclined.

The posterior bar is longer than the anterior, being fairly deep, shallowing
posteriorly, and bearing 4 or 5 triangular denticles which are laterally compressed
and posteriorly inclined.

In aboral view the unit is excavated beneath the apical denticle and the posterior
bar, the cavity having flared lips. Beneath the anterior bar there is a narrowing
groove.

Remarks. This species is very similar to P. laevipostica (Rexroad & Collinson)
which should be referred to the genus Prioniodina. The two species differ in the
degree of curvature of the anterior bar, our species being much less curved, and in the
dentition of the posterior bar, on which P. laevipostica bears 4 or 5 well-formed
denticles. The obvious morphological similarities of these two species lead us to
believe that P. prelaevipostica is the precursor of P. laevipostica.

i 9 8 BRITISH AVONIAN CONODONT FAUNAS

Prioniodina stipans (Rexroad)
Plate 28, figs. 7a-ioc

1957 Subbryantodus stipans Rexroad : 39, PI. 4, fig. 1.

1961 Subbryantodus stipans Rexroad ; Higgins : 219, text-fig. 6, PI. 12, fig. 14.

1962 Subbryantodus stipans Rexroad ; Higgins : 13, text-fig. 2, PI. 1, fig. 9.

Material. 105 specimens : figured, X 337-X 340.
Range. North Crop 3D 10-3D 22.

Description. The most distinctive features of this species are the relatively
short but strongly curved general form, with a series of subequal pointed denticles,
the apical denticle being only slightly larger than those of its neighbours, and the
wide flaring and greatly longitudinally extended basal cavity.

The basal cavity is greatly elongated and extends almost to the posterior end of the
posterior bar, and about two-thirds the way to the end of the anterior bar. It is
biconvex in outline, very deep, and slightly asymmetrical, with thin lateral edges.
The anterior bar is about equal in length to the posterior, but is rather deeper,
although it decreases slightly in depth anteriorly. The whole basal margin of the
unit is deeply concave in inner lateral view and the anterior bar is conspicuously
bowed inward. There is a rather inconspicuous shoulder developed about two-thirds
of the height from the aboral margin to the base of the denticles. The anterior bar
bears a series of about 12 denticles, confluent for most of their length, but bluntly
pointed in their free apices. They have strongly convex lateral faces in their free
portions and flat to gently convex lateral faces in their confluent portions, their free
edges being more or less sharp. Those in the posterior two-thirds of the bar are of
more or less uniform height and are regularly inclined posteriorly at about 45 ° to the
bar, but those in the anterior third of the bar decrease in height towards the anterior
end, and the most anterior two or three denticles are relatively inconspicuous and
wholly confluent.

The apical denticle is about twice as wide as the adjacent denticles, and is about
twice as long as adjacent denticles of the anterior and posterior bars. It is inclined
at about 45 ° to the adjacent aboral surface.

The posterior bar is sharply recurved and bears a series of about 7 sharply pointed
and partly fused denticles, which are strongly laterally compressed, and which tend
to decrease in size posteriorly, especially in the posterior third.

Prioniodina subaequalis (Higgins)
Plate 28, figs, ia-4

1961 Subbryantodus subaequalis Higgins : 218-219, PI- I2 > fig- *5> text-fig. 6.
1963 Subbryantodus subaequalis Higgins ; Bouckaert & Higgins : 17, fig. 3.
Subbryantodus subaequalis Higgins ; Collinson & Druce (in press).

Material. 143 specimens : figured, X 341-X 344.
Range. North Crop 3D 10-3D 22.

BRITISH AVONIAN CONODONT FAUNAS 199

Description. The most striking features of this species are the confluent denticles
of the long anterior bar, and the large denticles of the posterior bar. There is no
conspicuous apical denticle, and the denticles of the posterior bar are discrete.

In aboral view the unit is straight in its median two-thirds, but both the anterior
and the posterior ends are sharply flexed inwards. There is a deep and relatively
conspicuous basal cavity below the apical denticle, and this is extended as a wide
deep groove along the greater length of the anterior bar, and as a shorter narrowing
groove below about half the length of the posterior bar. The edges of the cavity and
of the aboral surfaces of the bars are relatively thin.

This is a somewhat variable species, but the anterior bar is generally rather longer
and deeper than the posterior, and tends to be rather straight along its aboral margin
when seen in inner lateral view. It bears a series of 9 or 10 laterally compressed
denticles which are confluent at their bases and which are inclined posteriorly. In
some specimens they show an alteration in size, and they also show a general tendency
to increase in size posteriorly. Their free edges are sharp and their lateral faces are
strongly convex, especially in the posterior half of the anterior bar. They show
some variation, in that in some specimens they are free for the greater part of their
length, but this is a relatively unusual feature.

There is no apical denticle in the strict sense, but the 2 or 3 denticles at the point
of flexure of the unit tend to be larger than any of the other, and to be more or less
equal in size. They are free for most of their length and they are inclined posteriorly,
the degree of inclination increasing towards the posterior end of the series. They
have sharp anterior and posterior edges and all taper sharply to their pointed tips.
They have gently convex lateral faces. Behind them is a series of up to 5 discrete
and strongly posteriorly inclined denticles, which in some specimens have smaller
denticles separating them. There is a rather indistinct apical lip at the point of
flexure. The posterior bar tends to decrease in depth posteriorly and its posterior
aboral margin is gently curved.

Prioniodina ? sp. nov.
Plate 28, figs. 6a-c

Material, i specimen : figured, X 345.

Range. Scotland GILM 3.

Description. A single specimen is tentatively referred to the genus Prioniodina.
It is characterized by an elongate straight anterior bar, which is continuous, without
any vertical flexure with the straight, but broken, posterior bar. The anterior bar
has convex lateral shoulders on the inner lateral face, and a straight inner lateral face
below them. Its oral surface bears 5 discrete short denticles with sharply pointed
tips, and posterior edges which are sharp ; they taper uniformly from their point of
origin and stand more or less erect or only slightly inclined to the anterior bar.
They show a slight tendency to increase in height posteriorly. The posterior bar
bears at least 3 closely spaced, but discrete, sharply-pointed denticles. That
nearest to the apical denticle is larger than the other two. They are strongly

2oo BRITISH AVONIAN CONODONT FAUNAS

laterally compressed, with sharp anterior and posterior edges and gently convex
lateral faces. The apical denticle is about three times as wide as the adjacent
denticles and two to three times as long. Its sharp anterior and posterior edges
taper uniformly to a point and it is gently inclined to the posterior bar. Along the
whole inner lateral length of the anterior and posterior bars there is a more or less
conspicuously convex shoulder below the point of origin of the denticles. In outer
lateral view the whole unit is somewhat natter and the denticles are seen to curve
slightly inwards. In aboral view the unit is excavated by a thin slit, which is very
narrow anteriorly, but which increases regularly in width posteriorly, being widest
posterior to the apical denticle, though there is no sign of lateral flare on the edges
below the apical denticle.

Genus PSEUDOPOLYGNATHUS Branson & Mehl 1934

1934 Pseudopolygnathus Branson & Mehl : 297.
1939 Macropolygnathus Cooper : 392.

Type species. Pseudopolygnathus prima Branson & Mehl 1934.

The origin and nature of the genus

Pseudopolygnathus developed from Spathognathodus in the late Devonian and early
Mississippian. Spathognathodus anteposicornis , S. plumulus plumulus sp. nov. and
S. aculeatus have lateral denticles developed on one side of the blade and 5. costatus
sulciferus has lateral denticles on both sides of the blade. Branson and Mehl (1934A :
298) have reported a series of specimens which are transitional between Spatho-
gnathodus and Pseudopolygnathus. Voges (1959 : 296, fig. 4, & 297, fig. 5) has also
illustrated a similar transitional series in the west German Cu I faunas.

Homoeomorphy among recurrent laterally nodose spathognathodids within the
present fauna, is discussed below (p. 239). Thus, since the laterally nOdose spatho-
gnathodids are homoeomorphic, and at least three chronologically distinct evolu-
tionary lines have been demonstrated, it follows that the genus Pseudopolygnathus is
polyphyletic.

This can be seen in our faunas. A Lower K Zone species is known, but there is then
a complete absence of pseudopolygnathids until the Upper Z Zone is reached in the
North Crop, and the Lower Z Zone in the Avon Gorge.

The Lower K Zone forms probably arose from the platform evolution of Upper
Devonian to VI nodose spathognathodids. The Upper Z Zone forms, however, can
be seen to have evolved directly from forms herein called S. costatus sulciferus, which
are stratigraphically restricted to the lower and middle parts of the Z Zone.

Homoeomorphy and taxonomy

As in the spathognathodids, the existence of homoeomorphy in the pseudopoly-
gnathids involves some problems in nomenclature. Since, however, most species of
the genus were described by E. R. Branson (1934) from the Hannibal Formation of
Missouri, in association with forms such as S. costatus sulciferus, it is probable that

BRITISH AVONIAN CONODONT FAUNAS 201

our upper two forms are part of the same phylogeny and should be referred to
Branson's species, whereas the homoeomorphic Lower K Zone forms are of distinct
origin and are best regarded as new species.

Affinities

Hass and others have considered that Macropolygnathus Cooper, 1939 is a junior
subjective synonym of Polygnathus Hinde, 1879. The basal cavity of Macropoly-
gnathus ithns, the type species of Macropolygnathus, is more akin to Pseudopoly-
gnathus than to Polygnathus, and transitional forms have been found between M.
ithus and P. fusiformis. We have, therefore, placed Macropolygnathus in synonomy
with Pseudopolygnathus.

Pseudopolygnathus is distinguished from Polygnathus by its laterally expanded
basal cavity.

Orientation

In Pseudopolygnathus primus, the curvature of the longitudinal axis of the cono-
dont and the shape of the basal cavity are bilaterally symmetrical elements. The
ornamentation of the platform and a cross section through the blade, near the
platform, are bilaterally asymmetrical elements.

The inner side of the conodont is concave and the outer side is convex. Forms are
designated as right or left, when orientated with the blade placed in front and the
convex side to the outside.

Posterior

True blode
posterior

Outer side

Trough

Posterior keel

Basal cavity

'Lips'
Anterior keel

Aboral view

Fig. 39. Pseudopolygnathus sp. showing morphological terms used in the text.

202 BRITISH AVONIAN CONODONT FAUNAS

THE EVOLUTIONARY DEVELOPMENT OF PSEUDOPOLYGNATHUS

There have been three distinct developments of the genus Pseudopolygnathus in
the Avon Gorge : one in the lower and middle parts of the K Zone, referred to as the
Pseudopolygnathus vogesi sp. nov. development, a second near the base of Z, the
Pseudopolygnathus primus development and a third in the upper part of the Z Zone
the Pseudopolygnathus midtistriatus development.

The three developments have been along similar lines, the starting point of each
being a straight, bladed spathognathodid with lateral denticles. Specimens of
growth series from the three developments are, with the exception of adults,
extremely difficult to distinguish (Fig. 43).

The evolution of pseudopolygnathus primus

Voges (1959) noted that in the Upper Devonian the Spathognathodus costatus
(sensu Bischoff & Ziegler) group marks the starting point in the evolutionary develop-
ment of Pseudopolygnathus primus, and other pseudopolygnathids, which deviate
from the typical bilateral symmetry of the spathognathodids. Voges recognized
two groups within the Spathognathodus costatus group, right forms and left forms, the
basal cavities of which are bilaterally symmetrical elements. The outer margin of
the platform of right forms and the inner margin of left forms are both convex, and
are thus bilaterally asymmetrical elements. In the left forms, there is a row of
nodes or ridges on the inner side of the platform, which extends for three quarters the
length of the unit. In the right forms, this row of nodes or ridges is on the outer side
of the platform. In left forms, nodes are usually absent on the outer side of the
platform, but in large specimens one or two nodes may be present on the outer side of
the platform, situated near the basal cavity. Voges recognized two varieties of right
forms, which correspond to the subspecies Spathognathodus spinulicostatus spinuli-
costatus (Bischoff 1957) and S. spinulicostatus ultimus (Bischoff 1957). In both these
subspecies a secondary row of nodes or small ribs extends from the middle of the
basal cavity to the posterior extremity on the inner side of the platform. In
Spathognathodus spinulicostatus ultimus they are more strongly developed, and a
furrow replaces the nodes along the posterior third of the blade.

Voges believed that S. spinulicostatus spinulicostatus and S. spinulicostatus ultimus
were stages in the ontogenetic development of a right form, to which Spathognathodus
costatus may be added as a left form. The opinion of Voges that S. spinulicostatus
ultimus may represent an ontogenetic senile form of S. spinulicostatus spinulicostatus
developed in the Wocklumeria Stage is not held by Ziegler (1962) who thinks it is
unlikely that a fauna consisting entirely of senile members of 5. costatus (spinuli-
costatus) spinidicostatus occurs at one horizon, while at a stratigraphically lower
horizon, it consists entirely of non-senile members of S. costatus (spinulicostatus)
spinidicostatus. In addition, Ziegler has found a few specimens of right forms of S.
costatus costatus and a few left forms of S. costatus (spinulicostatus) spinidicostatus and
5. costatus (spinulicostatus) ultimus.

Voges believed that from the first stage, represented by the S. costatus group, there

BRITISH AVONIAN CONODONT FAUNAS

203

develops a second stage, represented by Pseudopolygnathns dentilineatus (see Voges
1959 : 297, fig. 5). In this second stage the outer margin of the platform of right
forms and the inner margin of the platform of left forms are convex, and they are
thus bilaterally asymmetrical elements. The outer part of the platform of left
forms and the inner part of the platform of right forms consist of a few nodes,
confined to the posterior part of the platforms. The basal cavities of right and left
forms are bilaterally symmetrical elements. The two halves of the basal cavity are
unlike in form, being characterized on the outside by a fold of the margin and a
lip-like indentation of the edge. This form of the basal cavity is retained during
further developments of the oral surface of the Pseudopolygnathus primus group.

Specimens of P. dentilineatus from the P. dentilineatus development of Voges, are
very similar to specimens of Pseudopolygnathus from the lower and middle parts of
the K Zone of the Avonian. These specimens are here referred to as Pseudopoly-
gnathus vogesi sp. nov. and are typical of the Cu I stage of the Sauerland (Voges 1959).
This is the lowest development of Pseudopolygnathus in the Avonian.

Voges was able to see the following further development of his Sauerland pseudo-
polygnathid faunas. The nodes and ridges of the outer part of the platform in left
forms, and on the inner part of the platform in right forms, extend towards the
anterior end and nearer the anterior extremity of the opposite side of the platform.
In addition, a symmetrical element is present in the ornament of the platform, when
the inner anterior angle of the platform becomes accentuated. P. foliaceus E. R.
Branson, and P. apetodus Cooper are representatives of this stage.

The stage represented by P. foliaceus and P. apetodus develops into P. triangulus
inaequalis and P. triangulus triangulus, which in the details of surface ornamentation,
is a symmetrical element. In P. triangulus, the conspicuous asymmetry has
disappeared and only the thickening of the blade near the platform on the right side,
which is higher on the blade than the left, remains.

In the uppermost part of the K Zone of the Avonian, no specimens of Pseudopoly-
gnathus have been found. There is a second development of Pseudopolygnathus — the
P. primus development — near the base of the Zi Limestone. The specimens of this
development are similar, but not identical, to specimens from the stage in Voges 's
development, which he described as including ' specimens similar to Pseudopoly-

Fig. 40. Diagram to illustrate the ontogenetic development of pseudopolygna.thids in

the Zi Subzone of the Avonian.

-"»

BRITISH AYONIAN CONODONT FAUNAS

gnathus foliaceaus and Pseudopolygnathus apetodus '. They also closely resemble P.
primus E. R. Branson, which occurs in the Chappel Limestone of Texas (Hass 1959).

The starting point for the P. primus development in the Avonian are specimens
here referred to as Spathognathodus costatus costatus, which are found in the upper
part of the K Zone and the base of the Z Zone. Forms with a row of lateral denticles,
here referred to as Spathognathodus costatus costatus E. R. Branson, (they are not
identical to Spathognathodus bischoffi sp. no v., but are homoeomorphs of the latter
species) develop a ridge on the outer side of the left forms and on the inner side of the
right forms. The edge of the ridge becomes crenulate and, at a later stage, nodes
develop at the posterior extremity. The next stage is marked by an increase in the
number of nodes along the ridge towards the anterior. The anterior extremity, on
the outer side of the left forms and on the inner side of the right forms, extends as far
anteriorly, as it does on the inner side of left forms and on the outer side of right
forms. A small trough is present between the carina and the nodes of the ridge on
the outer side of right forms and on the inner side of left forms. The nodes on the
outer side of right forms, and on the inner side of left forms, become elongated to form
ridges in later development, as also, in further development, do the anterior nodes of
the outer side of left forms and on the inner side of right forms. Many bizarre forms
can be formed as a result of the thickening of the ribs, but in most adults the trough
at the anterior extremity of the outer side of left forms and on the inner side of right
forms can still be detected.

A count was made of specimens of Pseudopolygnathus from a horizon 65 feet above

4/ 4/ 4, 4/ 5/5/5/5/ 6/ & S, 6/ 7, 7. 1, 7, 8/ 8/ 8/ 8/

7 1 x 2 '3 <4 M x 2 7 3 x 4 A '2 7 3 '4 X 1 '2 / 3 /» M 4 ^3 X 4

NO. OF

SPECIMENS

-1
-2
-3
-4
-5
-6

4
/ 3

Number of nodes on right side of platform.

Left side of the platform expanded

Left side of the platform expanded with crenulate edge

Left side of the platform has nodes at the posterior and a trough ot the anterior

Left side of the platform is nodose

Ridges on both sides of the platform.

Fig. 41. Frequency diagram showing variation in the number of nodes and platform
ridges in relation to platform shape in growth stages of a pseudopolygnathid population
from a sample 65 ft. above the base of Zi in the Avon Gorge.

BRITISH AVONIAN CONODONT FAUNAS

205

the base of the Zi Limestone in the Avon Gorge. The number of denticles on the
right side ^of the platform was plotted, and also the character of the left side of the
platform as marked by a a ridge, b a crenulated ridge, c a few denticles at the posterior
and a trough at the anterior, or d nodes along its entire length. Adults were identi-
fied by the presence of ridges on both sides of the platform. The results showed that

a. Forms with 4 nodes on the right side of the platform had either a ridge, or a

crenulate ridge on the left side of the platform. No specimens were seen which
had 4 nodes on the right side and nodes on the left side.

b. Forms with 5 nodes on the right side of the platform had either a crenulate ridge,

or a few denticles at the posterior end and a trough at the anterior end. No
specimens were found with a straight edge to the ridge, or with denticles
continuous on the left side.

c. Forms with 6 denticles on the right side had either a few denticles at the posterior

extremity of the left side and a trough at the anterior extremity, or they had a

continuous row of denticles on the left side.
A similar plot was made of specimens higher in the section from Sample Z 21 at the
base of Z2 (fig. 25b). In this sample fewer specimens with 4 nodes on the right side
of the platform were present (4%, as opposed to 25% in the lower horizon.)

Ay At Ay Ay
'\ '2 '3 '4

5/5/5/5, 6/6/6/6/ 7, 7, 7, 7,

"l '2 '3 / A A '2 x 3 / A / \ '2 / 3 'A

NO. OF
SPECIMENS

-6

Number of node* on the right side of the platform.
Left side of the platform expanded-

Left side of the platform expanded with a crenulate edge.

Left side of the platform has nodes at the posterior and a trough at the anterior
Left side of the platform is nodose.
Ridges on both sides of the platform

Fig. 42. Frequency diagram showing variation in the number of nodes and platform
ridges in relation to platform shape in growth stages of a pseudopolygnathid population
from Sample Z 21 at the base of the Z2 Subzone of the Avon Gorge.

206 BRITISH AVONIAN CONODONT FAUNAS

This seems to indicate that the number of denticles on the right side of the platform
is indicative of the ontogenetic age of the specimen and that the age is also reflected
on the left side by the stage of development, through ridge, crenulated ridge, nodose
posterior part of ridge and a continuously nodose ridge, culminating with the
presence of ridges on both sides of the platform.

The stage of development in Voges's fauna represented by Pseudopolygnathus
tricing ul us inaequalis and Pseudopolygnathus triangulus triangulus, which developed
from the stage represented by Pseudopolygnathus foliaceus and Pseudopolygnathus
apetodus, is not present in the Avonian. In the Avonian, specimens of Pseudopoly-
gnathus primus are developed which consist of 7 ridges on the right side of the platform
and a number of nodes confined to the outer margin on the left side of the platform,
with a trough developed between the carina and the nodes of the left side of the
platform. With further development, the nodes on the outer margin of the left side
of the platform extend towards the carina to become ridges similar in outline to those
on the right side of the platform. This development starts at first at the posterior
end and extends towards the anterior, with the result that the platform on both sides
of the carina consists of a number of ridges. The left side of the platform never
extends as far to the anterior as the right side of the platform. In addition, a faint
trace of a trough is present at the side of the carina, even in adult specimens. These
forms are identical to Pseudopolygnathus multistriatus (Mehl and Thomas).

Higher in the section forms here referred to Pseudopolygnathus cf. longiposticus
appear and they have the same outline as advanced species of P. primus ; it is
suggested, therefore, that they may represent a further stage in the development of
Pseudopolygnathus.

The third development of Pseudopolygnathus in the Avonian — P. multistriatus
development — takes place in Z2. The specimen illustrated by Hass (1959, PI. 47,
fig. 21) as a juvenile of Pseudopolygnathus lanceolatus is a straight-bladed spatho-
gnathodid, with three lateral denticles. From such individuals the ontogenetic
growth stages illustrated by Hass lead to the development of P. multistriatus.

In juveniles (which resemble Spathognathodus tridentatus) the denticles are
developed on one side of the platform only ; the opposite side develops at first by the
formation of a slight ridge and, later, by the development of nodes on the ridge. A
slight trough is again present on one side and this side is not developed as far to the
anterior as is the other. Later development involves the replacement of nodes by
ridges, which in adults become coarse and irregular.

Difficulty was experienced in the present study in separating juvenile specimens of
P. multistriatus from adult specimens of Pseudopolygnathus dentilineatus. Specimens
in the ontogenetic sequence of P. multistriatus, which are similar to Pseudopoly-
gnathus striatus Mehl and Thomas, are identical to P. dentilineatus of Ziegler (1962).
Bischoff (1957) and Voges (1959) include P. striatus in synonomy with P. dentilineatus.
In view of the fauna associated with P. striatus, including Gnathodus texanus and
Gnathodus cuneiformis, it seems likely that Rexroad and Scott's (1964) interpretation
in placing P. striatus in synonomy with P. multistriatus is correct. This difference

BRITISH AVONIAN CONODONT FAUNAS

207

Pseudopolygnathus
multistnatus

Pseudopolygnathus
Pseudopolygnathus multistnatus
multistnatus

Spathognathodus

costatus
sensu ER Branson

Pseudopolygnathus
dentihneatus (juvenile)

Pseudopolygnathus

.. dentihneatus

Pseudopolygnathus

dentihneatus-

Pseudopolygnathus
primus

Pseudopolygnathus
vogesi.

Spathognathodus

spinuhcostatus

sensu Ziegler

Spathognathodus

costatus

sensu Ziegler

Spathognathodus
aculeatus

Fig. 43. Phylogeny of the genus Pseudopolygnathus and related forms in the Avonian.
Vertical lines : stratigraphic range. Full arrows : phylogenetic development. Half
arrows : morphological variation at one horizon.

20S BRITISH AYONIAN CONODONT FAUNAS

in synonomy may explain the different stratigraphic ranges in North America and
Germany for the two species in question.

Pseudopolygnathus dentilineatus E. R. Branson
Plate 5, figs. o,a-i3C. Plate 6, figs. 8a-c

1934 Pseudopolygnathus dentilineata E. R. Branson : 317, PL 26, fig. 22.
?I934 Pseudopolygnathus varicostata E. R. Branson : 318, PI. 26, figs. 19, 20.
1934 Pseudopolygnathus subrugosa E. R. Branson : 318, PI. 26, fig. 18.
1934 Pseudopolygnathus projecta E. R. Branson : 320, PI. 26, figs. 10, 11.
1934 Pseudopolygnallms brevimarginata E. R. Branson : 319, PI. 26, fig. 3.
?i939 Pseudopolygnathus varicostata E. R. Branson ; Cooper : 408-409, PI. 40, figs. 44-45.
?i956 Pseudopolygnathus striata Mehl & Thomas ; Bischoff & Ziegler : 164, PI. 11, fig. 20.
non 1957 Pseudopolygnathus dentilineata E. R. Branson ; Bischoff : 50, 51, PI. 4, figs. 30-32,

( = Pseudopolygnathus vogesi sp. nov.) (PI. 4, fig. 29 = Pseudopolygnathus primus)
non 1959 Pseudopolygnathus dentilineata E. R. Branson ; Voges : 300-301, PI. 34, figs. 49,

50, text-fig. 511= Pseudopolygnathus vogesi sp. nov.
non 1962 Pseudopolygnathus dentilineata E. R. Branson ; Ziegler : PI. 2, figs. 10, 11.

Material. 182 specimens : figured, X 478, X 479, X 480, X 481, X 438, X 477.
Range. Avon Gorge Z 12-Z 28.

Description. This species is represented by pseudopolygnathids with an
asymmetrical platform. Both the right and the left sides of the platform are
ornamented with 4 to 7 nodes or ridges which are confined to the margin of the
platform. The basal cavity is a symmetrical element, with a fold on the inner
margin and a smooth convex outer margin in both right and left forms. The basal
cavity, as pointed out by Klapper (1966 : 15), is as wide as the platform in aboral
view.

This species has bilaterally asymmetrical right and left forms. The platform is
two and a half times as long as wide, being widest at the anterior and narrowing to
the pointed posterior. In adult specimens the platform is less triangular and more
oval in outline. The margin of the right side of the platform in both right and left
forms is convex and widest at mid-length : that of the left side of the platform is
widest close to the anterior and narrows to the pointed posterior. The right side of
the platform in both right and left forms extends further to the anterior than does the
left side. The platform on either side of the carina is ornamented by 4 to 7 nodes or
ridges, which are confined to the margin. There is usually one more node present on
the right side of the platform than on the left. In smaller specimens a distinct
trough may be present between the denticles of the margin and the carina, in the
anterior half of the left side of the platform. A central straight to slightly curved
nodose carina runs the length of the platform. The nodes of the anterior portion of
the carina are stubby and wider than those of the posterior, which are more distinct
and erect. The carina in smaller specimens extends a short distance beyond the
posterior extremity of the platform.

The anterior blade, commonly composed of 6 denticles, is highest at the anterior
end and slopes uniformly to the posterior.

BRITISH AVONIAN CONODONT FAUNAS 209

In aboral view the basal cavity is large and occupies the anterior half of the
platform ; the outer side of the margin has a slight fold. The basal cavities of right
and left forms are bilaterally symmetrical elements.

Remarks. In the basal beds of the Z Zone specimens of P. primus occur, which
resemble P. dentilineatus in outline, but which differ in detail because the nodes or
ridges of the right side of the platform are not confined to the margin, as in P.
dentilineatus, but are elongated and extend into the carina. Also in adult P. primus
there is a greater number of ridges than in adult P. dentilineatus. The anterior
trough on the left side of the platform is present in both P. dentilineatus and P.
primus, but in the latter species the nodes at the posterior of the left side of the
platform are extended to the carina and form ridges. In addition the basal cavity is
as wide as the platform in P. dentilineatus, but less wide in P. primus.

Higher in the section, forms resembling P. dentilineatus are found, but it is thought
that they represent growth stages of other pseudopolygnathids. P. striatus Mehl and
Thomas, for example, is similar to P. dentilineatus but can be shown by ontogenetic
studies to be a growth stage of P. multistriatus.

We agree with Klapper (1966 : 15) that P. dentilineatus developed from double
rowed forms of Spathognathodus. We do not regard S. costatus ultimus as their direct
ancestor.

Pseudopolygnathus expansus sp. nov.
Plate 5, figs. 2a-c, 4a-c

Derivation of name. After the expanded anterior part of the platform.

Diagnosis. Pseudopolygnathid with straight axis in the mid and anterior thirds,
but curved in the posterior third. Anterior third of the right platform is expanded.
Outer margin, except expanded part, has convex outline and is ornamented by nine
or more transverse ridges. Anterior to mid length of unit, margin of inner side of
platform is expanded for a short distance. Basal cavity is asymmetrically flared ;
both inner and outer anterior margins of basal cavity expanded laterally, but that of
outer margin is greater.

Material. 3 specimens : Holotype X 483, Paratype X 482 (both figured).

Type locality and horizon. Avon Gorge, the middle of the K Zone. Sample
K 12.

Range. Avon Gorge, K 12.

Description. The platform is lanceolate in outline. The axis of the unit is
straight in the mid and anterior thirds, but curved in the posterior third. The
platform is widest anterior to mid-length and is two to three times as long as wide.
The convex margin of the outer side of the platform is interrupted by a lateral
expansion of the platform, mid-way between the anterior edge and the mid-length of
the unit. The outline of the inner margin posterior to the mid-length is straight to
slightly convex. At the mid-length the inner platform is expanded and tapers
gradually from the expanded portion to the anterior extremity. The outer side of
the platform is ornamented by up to nine transverse ridges, extending from the

.mo BRITISH AVONIAN CONODONT FAUNAS

margin to the carina. The inner side of the platform is ornamented by up to eleven
ridges, the posterior two being nodose at the margin ; the ridges in the posterior half
of the inner platform extend to the carina from the margin. Those of the anterior
half do not reach the carina and a trough is present, which is open to the anterior.
The anterior edge of the inner part of the platform is lower on the carina than is the
anterior edge of the outer part of the platform, which is at the same level as the
carina. The 4 posterior denticles of the carina are nodose, but the remainder of the
carina is composed of fused denticles.

The basal cavity is asymmetrical, pointed posteriorly and rounded anteriorly.
Both the inner and outer margins of the basal cavity are expanded laterally in the
anterior half. The anterior blade is of unknown form.

Remarks. Pseudopolygnathus expansus sp. nov. is closely related to Pseudopoly-
gnathus vogesi sp. nov. and transitional specimens have been found (PI. 5, fig. 6-7), but
is distinguished from it by the expanded anterior portion of the outer side of the
platform. In this respect it resembles P. primus and is interpreted here as a homoeo-
morph of the latter species.

Pseudopolygnathus cf. fusiformis Branson & Mehl

Plate 6, fig. 1

1934 Pseudopolygnathus fusiformis Branson & Mehl : 298, PI. 23, figs. 1-3.

Material, i specimen : figured, X 552.

Range. Avon Gorge, C 14.

Description. A narrow platform is developed on either side of the strongly
denticulate carina. The platform is widest anteriorly and tapers uniformly to the
pointed posterior. In lateral view the platform is arched. The margins of the
platform are notched and edged by 5 or 6 nodes. The blade is almost as long as the
platform, and contains 7 denticles, which are fused with the high denticles of the
carina. The carina is continued a short distance beyond the posterior extremity and
bears 2 or 3 denticles. Aborally, there is a large basal cavity, typical of Pseudopoly-
gnathus, which extends anteriorly to the junction of the blade and platform. It is
rounded anteriorly and pointed posteriorly.

Remarks. The specimen most closely resembles Pseudopolygnathus fusiformis
Branson & Mehl, but it may be a juvenile of Polygnathus.

Pseudopolygnathus cf. longiposticus Branson & Mehl

Plate 30, figs. 3, 7, 9-17

1934 Polygnathus longipostica Branson & Mehl : 294, 311, PI. 24, figs. 8-11.

Material. 107 specimens : figured, X 522, X 523, X 433, X 434, X 545, X 442,
X 443, X 448, X 449, X 547.

Range. Avon Gorge Z 11-C 7.

BRITISH AVONIAN CONODONT FAUNAS 211

Description. The unit is straight, the platform being about twice as long as the
blade. It is widest near mid-length and tapers to the posterior. The central carina
is nodose and is continued a short distance beyond the posterior edge. One of the
nodes of the carina near the posterior is higher than the others. The platform is
ornamented by a number of short ridges near the outer margin, normal to the
carina. The troughs between the carina and the ridges are unornamented. The
anterior blade is high and composed of 5 fused denticles. In lateral view this species
has a characteristic outline. The oral edge is highest at the anterior and slopes
regularly to the posterior. The oral edge of the platform is arched convexly. The
aboral edge is strongly concavely arched. In aboral view there is a very large pit
and a strong keel.

Remarks. The present specimens, although very close to P. longiposticus, differ
in the outline of the platform, which more closely resembles that of Polygnathus
macrus Cooper and Polygnathus orthus Cooper.

Pseudopolygnathus multistriatus Mehl & Thomas
Plate 5, figs. 14-16. Plate 6, fig. 2

1947 Pseudopolygnathus multistriata Mehl & Thomas : 16, PI. 1, fig. 36.

1947 Pseudopolygnathus attenuata Mehl & Thomas : 17, PI. 1, fig. 9.

1947 Pseudopolygnathus rustica Mehl & Thomas : 17, PI. 1, fig. 8.

1947 Pseudopolygnathus striata Mehl & Thomas : 17, PI. 1, fig. 10.

1957 Pseudopolygnathus multistriata Mehl & Thomas ; Bischoff : 51, PI. 4, figs. 33, 35.

I 959 Pseudopolygnathus lanceolata Hass : 391, PI. 47, figs. 16—26.

1964 Pseudopolygnathus multistriata Mehl & Thomas ; Rexroad & Scott : 41, 42, PI. 2,
fig- 30-

Material. 46 specimens : figured, X 485, X 486, X 487, X 484.

Range. Avon Gorge Z 23-Z 29.

Description. This species is distinguished by the platform, which is not
markedly asymmetrical ; it is ornamented by transverse ridges, usually nine or more
on either side of the central carina. There is a short anterior blade, and a trough on
the side of the carina in the anterior part of the left side of the platform. Adult
specimens frequently have rough oral surfaces owing to the coarse nature of the
ornament.

The platform is three and a half times as long as wide and has convex margins.
The axis is straight to slightly curved and the platform on the left side of the carina
does not extend as far to the anterior, as does the platform on the right side. The
platform on either side of the carina is ornamented by 9 nodes which elongate into
ridges reaching the carina. A slight trace of a trough is, however, present in the
anterior part of the left side of the platform. The anterior two thirds of the carina
is composed of fused denticles, but in the posterior third the denticles of the carina
are free and distinct. The carina is continued a short distance beyond the posterior
extremity of the platform. The anterior blade, composed usually of 5 denticles, is
highest at the anterior and decreases in height to its junction with the carina. The

2i2 BRITISH AVONIAN CONODONT FAUNAS

anterior blade is also equal in height to its length, and is curved in the opposite
direction to the curvature of the posterior extension of the carina. The basal cavity,
situated in the anterior part of the unit, is subcircular in outline, but more drawn out
to the posterior than the anterior. It is as wide as the platform in juveniles, but in
adults is less wide than the platform.

Remarks. This species developed from Pseudopolygnathus primus by the extension
of the nodes on the left side of the platform towards the anterior, and by a change in
the platform ornament from marginal nodes to transverse ridges.

Pseudopolygnathus striatus, P. rusticus, P. attenuatus and P. lanceolatus are all
considered to be growth stages of P. multistriatus. P. striatus is a homoeomorph of
P. dentilineatus, as pointed out by Klapper (1966 : 15).

Lower Z forms referred to P. dentilineatus in this study (PI. 6, fig. 8) resemble P.
multistriatus (PI. 5, fig. 16), but the left side of the platform is more strongly
developed, and also there are 8 nodes or ridges on the right side of the platform in
P. multistriatus.

The Avonian P. multistriatus pseudopolygnathids gave rise to P. cf. longiposticus.

Pseudopolygnathus nodomarginatus (E. R. Branson)
Plate 9, figs. ia-4c. Plate 12, figs. 6a-8c, ioa-c

1934 Polygnathus nodomarginata E. R. Branson 310, PI. 25, fig. 10.

1934 Pseudopolygnathus brevimarginata E. R. Branson 322, PI. 26, fig. 3.

1934 Pseudopolygnathus tenuis E. R. Branson 319, PI. 26, figs. 13, 14.

1938 Polygnathus flabella Branson & Mehl : 147, PI. 34, fig. 48.

!939 Polygnathus anida Cooper : 399, PI. 39, figs. 39, 40.

x 939 Polygnathus flabellum Branson & Mehl ; Cooper : 400, PI. 39, figs. 13, 14.

1944 Polygnathus flabella Branson & Mehl ; E. B. Branson : 208, 221, PI. 39, fig. 48.

1949 Polygnathus anida Cooper ; Thomas : 411, PI. 3, figs. 10, 11.

1950 Streptognathodus ? sp. Youngquist, Miller & Downs : 529, PI. 67, figs. 12-14.

195 1 Polygnathus aff. symmetrica Branson & Mehl ; Youngquist & Downs : 789, PI. 111,
fig. 6.

1956 Polygnathus inornata E. R. Branson ; Bischoff & Ziegler : 157, PI. 12, figs. 4, 5.

1957 Polygnathus nodomarginata E. R. Branson ; Bischoff & Ziegler : 157, PI. 12, fig. 6.
J 959 Polygnathus cf. flabellum Branson & Mehl ; Voges : 290, PI. 34, figs. 8-1 1.

non 1959 Polygnathus nodomarginata E. R. Branson ; Helms : 251, PI. 3, figs, ia, b, c.
1966 Polygnathus nodomarginata E. R. Branson ; Jones & Druce : 358, fig. 3, No. 3.

Material. 323 specimens : figured, X 488, X 489, X 490, X 491, X 492, X 493,
X 494, X 495.

Range. North Crop ZLA 29-ZL 18.

Description. The platform is asymmetrical, one side being shorter than the
other. In juveniles it is ornamented by a lateral row of nodes on each margin with a
trough on either side of the medial carina (PI. 9, fig. 1) . With old age the rows of nodes
expand into a platform with transverse ridges and the troughs tend to shallow (e.g.
PI. 12, fig. 6a). The carina is coarsely nodose and extends posteriorly, the juveniles
often exhibiting a longer posterior free blade than the adults. The anterior blade is
about half the platform length ; the highest denticles are developed anteriorly and

BRITISH AVONIAN CONODONT FAUNAS 213

are just higher than the highest point of the platform in lateral view ; the blade is
made up of 7 to 8 fused, laterally compressed, denticles.

In aboral view the basal cavity is lanceolate, being widest at the anterior end of the
platform and narrowing gradually toward the posterior, where it becomes a narrow
groove in a deep keel.

Remarks. It appears that this species is closely related to P. lacinatus, the
platform ornament serving to distinguish them.

The most distinctive features of the present species are its more or less laterally
expanded basal cavity, its relatively strong ornament, and its relatively long blade.
The platform ranges from elongate pointed to broadly lanceolate in oral outline.

It is difficult to decide whether this species is better assigned to the genus Pseudo-
polygnathus or to the genus Polygnathus, but because some specimens possess typical
pseudopolygnathid cavities, it is here included in this genus.

Pseudopolygnathus postinodosus sp. nov.
Plate 6, figs. 6a-c

Derivation of name. After the high denticles of the posterior extension of the
carina.

Diagnosis. Pseudopolygnathus characterized by posterior extension of carina
bearing a few high denticles. Platform situated in mid-third of unit bears a few
indistinct nodes confined to convex margins. Anterior blade also distinctive, being
highest at mid length, sloping abruptly to posterior and more gently to anterior.
Basal cavity elongate with thickened lips.

Material. 3 specimens : Holotype X 496 (figured).

Type locality and horizon. Avon Gorge Z2 Limestones. Sample Z 38.

Range. Avon Gorge Z 13-Z38.

Description. In oral view the platform is seen to occupy the mid third of the
unit, the anterior blade the anterior third of the unit, and the posterior extension of
the carina the posterior third. The axis is straight to slightly curved and it is
possible to recognize right and left forms, although in the present study only right
forms have been found. The anterior blade is composed of 7 denticles ; the 3 at the
posterior are smaller than the other 4. The fourth anterior denticle is highest and
the third anterior denticle is only slightly lower than the fourth. The anterior two
denticles are, like the third and fourth, free for the greater part of their length, but
they are lower than the third and fourth denticles. The carina in the region of the
platform is low and consists of a number of stubby denticles, which are fused together.
At the posterior extremity of the platform the denticles of the carina become distinct,
and on the posterior extension there are a few distinct high denticles.

In lateral view the denticles of the anterior blade and of the posterior extension of
the carina are stout and spine-like. The three denticles of the posterior extension of
the carina are free from the base to the tips, and diverge at a wide angle from one
another. The anterior edge of the anterior blade and the posterior edge of the

2i 4 BRITISH AVONIAN CONODONT FAUNAS

posterior extension of the carina are of equal elevation. The four high anterior
denticles of the anterior blade give the anterior edge of the anterior blade a serrated
appearance. The low carina is raised slightly above the level of the platform.

The basal cavity is situated in the anterior part of the platform. It has an oval
outline, with very thick lips. It is slightly longer than wide and a narrow trough
runs from the pit to the posterior extremity of the platform. A keel runs from the
anterior extremity of the basal cavity to the anterior extremity of the unit.

Remarks. It is considered likely that Pseudopolygnathus postinodosus sp. nov.
developed from Spathognathodus sp. nov. by the continued development of a platform,
transitional specimens between the two species having been found. In these transi-
tional specimens a second row of nodes is developed on the inner side of the blade,
directly over the basal cavity. This development is in addition to the row of nodes
on the outer side of the blade (see Fig. 47).

Pseudopolygnathus primus Branson & Mehl
Plate 6, figs. 4a-5c, 7ioa-i2c

1934 Pseudopolygnathus prima Branson & Mehl : 298, PI. 24, figs. 24, 25.

1934 Pseudopolygnathus foliacea E. R. Branson : 316, PI. 26, figs. 27, 28.

1934 Pseudopolygnathus irregularis E. R. Branson : 316, PL 26, figs. 25, 26.

1934 Pseudopolygnathus corrugata E. R. Branson : 317, PI. 26, fig. 23.

1934 Pseudopolygnathus costata E. R. Branson : 317-318, PI. 26, fig. 21.

1934 Pseudopolygnathus distorta E. R. Branson : 318-319, PL 26, figs. 16, 17.

? 1934 Pseudopolygnathus varicosiata E. R. Branson : 318, PL 26, figs. 19, 20.

1934 Pseudopolygnathus sulcifera E. R. Branson : 319, PL 26, fig. 15.

1934 Pseudopolygnathus asymmetrica E. R. Branson : 320, PL 26, fig. 12.

1934 Pseudopolygnathus inequicostata E. R. Branson : 321, PL 26, fig. 6.

1934 Pseudopolygnathus crenulata E. R. Branson : 321, PL 26, figs. 4, 5, 7, 8.

1934 Pseudopolygnathus lobata E. R. Branson : 322, PL 26, figs. 1, 2.

1938 Pseudopolygnathus prima Branson & Mehl ; Branson & Mehl : PL 33, figs. 47, 48.

? 1938 Pseudopolygnathus varicostata E. R. Branson ; Branson & Mehl : 133, PL 33, figs. 25,
46.

1939 Polygnathus subserrata Branson & Mehl ; Cooper : 404, PL 39, figs. 75, 76 only.

J 939 Pseudopolygnathus asymmetrica E. R. Branson ; Cooper : 406-407, PL 40, figs. 23, 24,
59, 60, PL 41, figs. 13, 14.

1939 Pseudopolygnathus crenulata E. R. Branson ; Cooper : 407, PL 40, figs. 25-27.

? 1939 Pseudopolygnathus varicostata E. R. Branson ; Cooper : 408, PL 40, figs. 44, 45.

1939 Pseudopolygnathus prima E. R. Branson & Mehl ; Cooper : 408, PL 40, figs. 30, 31.

!939 Pseudopolygnathus irregularis Branson ; Cooper : 408, PL 40, figs. 21, 22, 35, 36.

J 939 Pseudopolygnathus distorta E. R. Branson ; Cooper : 408-409, PL 40, figs. 49-50.

1944 Pseudopolygnathus prima Branson & Mehl ; Branson & Mehl : 244, PL 94, figs. 11, 12.

1944 Pseudopolygnathus prima Branson & Mehl ; Branson & Mehl : 181, PL 32, figs. 25, 26.

? 1944 Pseudopolygnathus varicostata E. R. Branson ; Branson & Mehl : 181, 222, PL 32,
figs. 25, 46.

1949 Pseudopolygnathus aurita Youngquist & Patterson : 67-68, PL 16, figs. 5, 6.

1949 Pseudopolygnathus carinata Youngquist & Patterson : 68, PL 16, fig. 4.

1949 Pseudopolygnathus irregularis Branson ; Youngquist & Patterson : 68-69, PL 16,

figs- i-3-
1949 Pseudopolygnathus prima Branson & Mehl ; Thomas : 412, PL 4, fig. 17.

BRITISH AVONIAN CONODONT FAUNAS 215

1949 Pseudopolygnathus cf. crenulata E. R. Branson ; Thomas : 412, PL 4, fig. 18.

1949 Pseudopolygnathus constrictiterminata Thomas : 428, PI. 4, fig. 16.

1949 Pseudopolygnathus cf. P. asymmetrica E. R. Branson ; Thomas : 436, PI. 3, fig. 42.

195 1 Pseudopolygnathus prima Branson & Mehl ; Hass : 2358, PI. 1, fig. 11.

1957 Pseudopolygnathus prima Branson & Mehl ; Cloud, Barnes & Hass : 813, PI. 5, fig. 10.

1957 Pseudopolygnathus irregularis Branson ; Bischoff : 51, PI. 6, figs. 12, 13.

1957 Pseudopolygnathus dentilineata E. R. Branson ; Bischoff : 50, 51, PL 4, fig. 29 only.

*959 Pseudopolygnathus prima Branson & Mehl ; Hass : PL 49, fig. 27.

J 959 Spathognathodus cf. costatus (E. R. Branson) Voges : 298, 299, PL 34, fig. 48 only.

1966 Pseudopolygnathus prima Branson & Mehl ; Klapper : 14, PL 4, fig. 8.

Material. 64 specimens : figured, X 546, X 497, X 498, X 499, X 500, X 549.

Range. Avon Gorge Z 13-Z 28.

Description. This species is extremely variable. All forms with an asym-
metrical platform, a narrow row of nodes or ridges on the right and left sides, but
with a flared anterior portion on the left, are referred to it. The basal cavity, accord-
ing to Klapper, is narrower than the platform, but not all our specimens of P. primus
agree with this.

The axis is arched, and right and left forms have been found which are bilaterally
asymmetrical elements. The platform is more strongly developed on the right side
than on the left in both right and left forms. The outer margin of the right side of
the platform is convexly curved and bears at least 7 nodes or ridges. The right side
of the platform is widest at mid-length, and tapers uniformly to the anterior and
posterior. The shorter left side of the platform consists of a smaller number of
nodes or ridges than the right side. The carina consists of fused denticles for the
greater part of its length, but there are a few distinct denticles at the posterior
extremity, where the carina is extended a short distance beyond the posterior end of
the platform.

The basal cavity is situated near the mid third of the unit, and is sub-circular in
outline with a fold on the inner margin and with a convex outer margin. A narrow
groove extends from the anterior extremity of the basal cavity to the posterior
extremity of the unit. The anterior edge of the unit, anterior to the basal cavity,
is sharp.

Remarks. Pseudopolygnathus primtis is similar in outline to P. dentilineatus, but
the platform ornamentation in the two species is different. The platform ornamen-
tation of P. primus has at least seven nodes or ridges on the right side, and ridges are
frequently present, whereas in Pseudopolygnathus dentilineatus there are nearly always
nodes which are confined to the margin ; ridges are rare and eight nodes or ridges on
the right side of the platform are unknown. Both margins of the platform in P.
dentilineatus are convex. In P. primus the margin of the left side of the platform is
more angular at the anterior than that of P. dentilineatus.

The development of P. primus has been described by Voges (1959) and again by
Klapper (1966). The writers agree with the opinion of Klapper (1966 : 14) that
there is a wide variety of surface ornamentation in P. primus, but that this can be
regarded as intraspecific variation.

216 BRITISH AVONIAN CONODONT FAUNAS

P. primus developed from P. dentilineatus in the Avonian. Three morphological
variations of P. primus have been observed : those with a wing-like expansion at
the anterior (PI. 6, fig. 10), those with a considerably larger right side to the platform
(PI. 6, fig. 7) and those where there is a distinct trough on the left side of the anterior
part of the platform (PI. 6, figs. 11, 12). This latter variation closely resembles P.
multistriatus and becomes the dominant form of P. primus in the middle part of the
Z Zone.

Pseudopolygnathus triangulus cf. pinnatus Voges
Plate 30, fig. 19

*959 Pseudopolygnathus triangula triangula Voges : 304, 305, PI. 35, figs. 7-13, p. 297, text-fig.

5 IV.
1963 Pseudopolygnathus triangula subsp. indet Voges ; Ziegler : PI. i, figs. 1, 2.
1963 Pseudopolygnathus triangula triangula Voges ; Ziegler : PI. 1, figs. 3, 4.

Material. 3 specimens : figured, X 502.
Range. Avon Gorge C 7.

Description. This species is characterized by having a platform with a triangular
outline. It is straight and wide at the anterior edge of the platform. The platform
in oral view is widest slightly anterior to its mid-length. It tapers gradually to the
posterior, having straight margins and a triangular posterior outline. Anterior to
the mid-length, the margin of the platform is gently curved and it tapers suddenly
to the anterior. The anterior blade is broken. The platform is one and a half times
as long as wide and has a straight axis. The oral surface of the platform is flat to
slightly concave and is ornamented by a number of ridges normal to the margin,
which are confined to the outer half of the platform and do not reach the carina.
The central carina is strongly developed and has knob-like projections on its upper
surface.

The aboral surface is flat and wide. The margins of the outer position are slightly
upturned. A strong keel runs the length of the unit, interrupted by the small
anteriorly situated pit of the basal cavity.

Remarks. The specimens found in the present study most closely resemble
Pseudopolygnathus triangula subsp. indet Ziegler (1963), but the anterior edge of the
platform is neither as straight nor as wide as it is in the type specimen (Voges 1959).
The present specimens have a more rounded anterior extremity.

Pseudopolygnathus vogesi sp. nov.
Plate 5, figs, ia-c, 3a-c, 5a-8

?i956 Pseudopolygnathus striata Mehl & Thomas ; Bischoff & Ziegler : 164, PI. 11, fig. 20.
?I957 Pseudopolygnathus dentilineata E. R. Branson ; Bischoff : 50, 51, PI. 4, figs. 30, 31,

32 only, (non PI. 4, fig. 29 = Pseudopolygnathus primus).
?I959 Pseudopolygnathus dentilineata E. R. Branson ; Voges : 297, text-fig. 5, fig. II, PI. 34,

figs- 49. 50.
?ig64 Pseudopolygnathus sp. Bouckaert & Ziegler : 27, PI. 4, fig. 12.

BRITISH AVONIAN CONODONT FAUNAS 217

Derivation of name. After Dr. A. Voges.

Diagnosis. Pseudopolygnathid with triangular platform, widest anteriorly,
tapering uniformly to pointed posterior. Usually 5 non-marginal bulbous nodes on
one side of the platform, and six on the other, confined to the margin. Carina
straight or slightly curved, bearing nodes fused towards anterior and free towards
posterior. Asymmetrical basal cavity occupying anterior half of platform has fold
developed on inner side of unit. Blade low and about equal in length to platform.

Material. 56 specimens : Holotype X 155, Paratype X 504, X 501, X 505,
X 507, X 506 (all figured).

Type locality and horizon. Avon Gorge, lower and middle part of the K Zone.
Sample K 12.

Range. Avon Gorge K 4-K 14, North Crop KL i-KL 5.

Description. The axis of the unit is straight or slightly curved. The carina
consists of 12 or more nodes, which are fused at the anterior and free at the posterior
end. The platform, which is two and a half times as long as its maximum width, is
widest anteriorly, there being an abrupt taper to the anterior extremity of the
platform. The margins are slightly convex in the anterior third and taper uniformly
to the pointed posterior. The posterior tip of the carina continues a short distance
beyond the posterior extremity of the platform. The outer side of the platform
extends slightly further to the anterior and is also slightly narrower than the other
side. It bears up to 5 bulbous nodes, which extend from the margin to the carina ;
the central node is widest and the anterior two are bigger than the posterior two.
The inner side of the platform has up to 6 bulbous nodes, which are smaller than
those of the opposite side of the platform. The anterior four nodes do not extend
to the carina and are confined to the margin. As a result, there is an anterior trough
present in the anterior part of the platform.

The outer side of the asymmetrical basal cavity is convex and the inner side has a
fold in the anterior part. The basal cavity is wide and occupies the anterior half of
the aboral surface. It is pointed posteriorly and rounded anteriorly. The anterior
blade consists of 5 or 6 denticles which are highest at mid-length.

Remarks. P. vogesi occurs in the lower and middle parts of the K Zone in the
Avon Gorge. It is a homoeomorph of ' Pseudopolygnathus dentilineata ' E. R.
Branson. It resembles P. dentilineatus as illustrated by Voges (1959 : 297, text-
fig. 5, n) which is characteristic of the lower part of Cu I in West Germany (Bischoff
1957, Voges 1959) and Pseudopolygnathns n. sp. of Bouckaert & Ziegler (1965 : 27,
PI. 4, fig. 12). In North America, the lowest stratigraphic occurrence of the genus
Pseudopolygnathus in the Mississippian is the occurrence of P. dentilineatus at the
base of the Glen Park Formation. P. dentilineatus ranges into the lower and middle
part of the Hannibal Formation in the Mississippi Valley (Collinson, Scott & Rexroad
1962).

Pseudopolygnathus vogesi sp. nov. is similar to P. expansus sp. nov. and transitional
specimens have been found.

218 BRITISH AVONIAN CONODONT FAUNAS

Pseudopolygnathus sp. A
Plate 6, fig. 3

Material. 6i specimens : figured, X 515.

Range. North Crop ZLA 29-ZLA 32.

Description. The specimen illustrated is very long and narrow. The platform
is extremely variable in its development and always highly irregular in outline.
Often it consists of irregular nodes rising out of the thickened medial part of the
unit ; sometimes these are fused to give a nodose platform of 3 to 4 denticles on
either side of the carina. Occasionally there are no nodes on the medial thickening.
The carina is very distinctive, consisting of sub-circular needle-like denticles standing
high above the platform. The anterior blade is very long and is a continuation of
the carina. In aboral view the basal cavity is elongate and asymmetrically flared.

Genus SCAPHIGNATHUS Ziegler i960
i960 Scaphignathus Ziegler : 403.

Type species. Scaphignathus velifera Ziegler i960.

The generic name and the type species were used, and the latter described, by
Helms (1959 : 655) who referred both to Ziegler 1959 as author. Ziegler's paper was
not published until i960, but subsequent authors have also attributed the genus to
him, and we follow this practice, which Article 50 of the Code of Zoological Nomen-
clature clearly allows.

Scaphignathus ? sp. A
Plate 2, figs. I3a-c

Material, i specimen : figured, X 532.

Range. North Crop ZL 2.

Description. The unit is boat-shaped, being asymmetrical with the anterior
blade developed on the right hand side when viewed posteriorly. The anterior blade
is broken in the only specimen. The platform is lanceolate, being widest at the
anterior, and is triangular in cross-section in the posterior portion. It is over twice
as long as wide, and is ornamented with low transverse ridges, terminating in low
nodes on the platform edge. Along the mid-line there runs a low nodose carina,
which joins the inner edge immediately posterior to the outer lateral blade, and then
runs as a low ridge anteriorly, joining the outer lateral blade and thus preventing the
trough from opening anteriorly.

In aboral view the cavity is large and asymmetrical, being expanded on the inner
side : the posterior part of the platform has a keel with a median groove.

Remarks. This form differs from Scaphignathus ? sp. B in that the oral trough
does not open anteriorly. The reasons for placing these two forms tentatively in the
genus Scaphignathus are given in the remarks following the description of S. sp. B.

BRITISH AVONIAN CONODONT FAUNAS

219

Platform
Carina \

Blade
1 Anterior

Posterior J^tCjiS » W /jjtlfc j

W^ffffif^nh^'

Outer side

Ridges

Oral view

Oral edge A

Platform_j£sSS^.s^.-^^s5;
Posterior ^^K*S^' '{%£/ %

'!.' '•'.' A Anterior
£^/-**3*«lade

Aboral edge

Lateral view

Fig. 44. Scaphignathus sp. showing morphological terms used in the text.

Scaphignathus ? sp. B
Plate 2, figs. i2a-c

Material. 3 specimens : figured, X 533.

Range. North Crop ZL 9-ZL 10, Avon Gorge Z 12.

Description. The only specimens present in our faunas have the posterior part
of the platform missing. The blade consists of 5 denticles of equal height, situated
on the right side of the platform when viewed from the posterior. The outer
platform ornament consists of low transverse ridges, giving a crenulate platform,
uniting with the inner side immediately posterior to the outer anterior blade, and
running as a low, non-denticulate inner blade not quite to the anterior of the unit.
It is separated from the outer lateral blade by a sulcus, which deepens anteriorly.

In aboral view the cavity is large and asymmetrical, being expanded on the inner
side. The unit is sub-triangular in cross-section and essentially boat-like.

Remarks. The presence of a median carina precludes the placing of these two
species in either Cavusgnathus or Clydagnathus and the basal cavity differs greatly
from the small basal cavity of Mestognathus. Scaphignathus has a small pit in adult
specimens but a large one in juveniles. Our specimens would appear to be adult but
are tentatively assigned to that genus.

Genus SIPHONODELLA Branson & Mehl

1934 Siphonognathus Branson & Mehl : 295 (non Richardson 1858).
1944 Siphonodella nom. nov. Branson & Mehl : 245.

Type species. Siphonognathus duplicata Branson & Mehl 1934.

22o BRITISH AVONIAN CONODONT FAUNAS

Siphonodella isosticha (Cooper)
Plate 12, figs. 9a, b, 11a, b

1930 Siphonognathus isosticha Cooper : 409, PI. 41, figs. 9, 10.

1962 Siphonodella n. sp. A Collinson, Scott & Rexroad : 7, fig. 4.

1962 Siphonodella obsoleta Cooper ; Miiller (partim) : 1388, fig. 4 only.

1964 Siphonodella isosticha (Cooper) Rexroad & Scott : 44, PI. 3, figs. 21-23.

1965 Siphonodella isosticha (Cooper) Ethington : 587, PI. 67, figs. 15, 17,

Material. 3 specimens : figured, X 534, X 535.

Range. North Crop KL 16-KL 19.

Description. The platform is narrow and elongate being broadest at its mid-
point. Ornament is lacking except for a medial nodose carina, two short anterior
rostral ridges, a few scattered nodes on the narrow inner platform, and incipient
transverse denticles on the margin of some specimens (PI. 12, fig. 11a). The basal
cavity is minute, and the whole unit keeled.

Remarks. Rexroad & Scott (1964 : 44) suggested that this species arose from
5. obsoleta Hass by reduction of the outer rostral ridge and platform ornament, but
they pointed out that the juveniles of the two species are very similar. All our
specimens appear to be young forms and they could be assigned either to S. obsoleta
or 5. isosticha, but absence of platform ornament in the largest specimen suggests
that they should be placed in S. isosticha.

Siphonodella obsoleta Hass
Plate 12, figs. I3a-c

J 959 Siphonodella obsoleta Hass : 392, PI. 47, figs. 1, 2.

1962 Siphonodella aff. S. obsoleta Hass ; Collinson, Scott & Rexroad : 7, chart 2.
1964 Siphonodella obsoleta Hass ; Rexroad & Scott : 45, PI. 3, fig. 25.

1964 Siphonodella obsoleta Hass [Nass in text] ; Budurov & Tschurnev : PI. V, figs. 5a-c,
11a, b, 13a, b, 14-17, 19.

Material. 2 specimens : figured, X 536.
Range. North Crop KL 16-KL 19.

Posterior

Platform

Loteral ridges

Outer side

Rostrol ridge

A ntenor blade

Fig. 45. Siphonodella sp. showing morphological terms used in the text.

BRITISH AVONIAN CONODONT FAUNAS 221

Description. The long outer rostral ridge distinguishes this species from S.
isosticha (Cooper). The ridge is situated on the outer platform and curves away
from the carina, paralleling the platform margin. It degenerates into a line of low
isolated nodes before becoming obsolescent near the posterior termination. The
inner platform bears irregular low nodes over the whole surface.

Siphonodella sp. A
Plate 12, figs. 12a, b

Material, i specimen : figured, X 537.
Range. North Crop KL 16.

Description. This specimen is a siphonodellid with a rounded posterior margin,
and a lobe developed on the posterior part of the outer side. The inner platform
possesses two longitudinal rostral ridges in its anterior part, the posterior part being
expanded laterally and ornamented with irregular low nodes, three of which replace
the carina, while others spread on to the outer platform. The outer platform
possesses a long rostral ridge, which covers the length of the platform and extends
along a lobe situated in the posterior part. The platform is unornamented except
for isolated nodes in the posterior.

In aboral view the unit is relatively flat and possesses a minute siphonodellid
cavity.

Remarks. This specimen is unlike any other described siphonodellid species. It
may be a pathologic variant of S. obsoleta Hass.

Siphonodella sp.
Plate 31, fig. 20

Material. 2 specimens : figured, X 539.

Range. Avon Gorge K 12-K 17.

Description. Two fractured specimens of the genus Siphonodella were found in
the Upper K Zone Beds. One specimen consists of the anterior quarter of the
platform, and the other of the anterior quarter of the platform and the anterior blade.
One of the specimens has one rostral ridge and the other two rostral ridges, developed
on either side of the carina. It is not possible to refer the specimens to any species.

Genus SPATHOGNATHODUS Branson & Mehl 1941

1856 Ctenognathits Pander (partim) : 32 (non Ctenognathus Fairmaire 1843).

J 933 Spathodus Branson & Mehl : 41 (non Spathodus Boulenger 1900).

1940 Pandorina Stauffer 428 (non Pandorina Bory de St. Vincent 1827, nee Scacchi 1833).

1941 Spathognathodus nom. nov. Branson & Mehl : 98, (pro Spathodus Branson & Mehl 1933).
1945 Mehlina Youngquist : 363.

1957 Ctenognathus (Pandorinellina) Muller & Miiller : 1083.
T 959 Pandorinellina Hass 378, (pro Pandorina Stauffer 1940).
1959 Branmehla Hass 381.

222 BRITISH AVONIAN CONODONT FAUNAS

1959 Ctenognathodus nom. nov. Fay : 195 (pro Ctenognathits Pander 1856).

1959 Ctenognathus (Ctenognathodus) Fay : 195.

1959 Ctenognathodus (Mehlina) Fay 195.

1962 Spathognathodus (Bispathodus) Miiller : 114.

Type species. Ctenognathus murchisoni Pander 1856.

The name Pandorinellina was first used by Miiller & Miiller (1957 : 1083) but was
clearly attributed by them to Hass in the (then forthcoming) Treatise. Article 50
of the Code of Zoological Nomenclature justifies the attribution of the genus to Hass.

Spathognathodus anteposicornis Scott
Plate 3, figs. 5a-8b

1961 Spathognathodus n. sp. A Scott & Collinson : 132, PI. 1, figs. 12-15.
1961 Spathognathodus anteposicornis Scott : 1224, text-fig. 2H - K.

Material. 59 specimens : figured, X 540, X 541, X 542, X 543.
Range. North Crop KL 19-ZLA 15, Avon Gorge K2 i-Z 28.

Description. The unit is elongate, being two to three times as long as the
highest anterior denticles ; it is straight in oral view, and highest at the anterior.
The anterior 3 denticles are the largest, standing twice as high as the remaining blade
denticles, the medial denticle of the three usually being highest. The remaining
denticles are of equal height over the medial third, gradually decreasing in size
posteriorly over the posterior third ; they are erect, basally fused and blunt tipped.
The aboral edge is straight (PI. 3, fig. 5a) to gently arched (PI. 3, fig. 7a). A lateral
denticle, sub-circular in cross-section, is developed high on the inner side of the unit
over the anterior portion of, or immediately anterior to, the basal cavity, the tip
generally being about equal in height to the adjacent denticles of the blade.

In aboral view the basal cavity is large and flaring, with an anterior pit. The
cavity occupies the median third and extends in both directions as an aboral groove.
The outer margin of the cavity is subcircular (PI. 3, fig. 5b) to biconvex (PI. 3, fig. 6b).

Remarks. Scott (1961 : 1224) described this species from the Louisiana Lime-
stone, which he regarded as Upper Devonian. Our specimens, which have a
restricted range above the Avonian occurrence of the genus Siphonodella, would
appear to be stratigraphically younger. Their occurrence in the present faunas may
be the result of one or more of at least three different factors : an independent
phylogenetic origin, so that they are homoeomorphs of Scott's S. anteposicornis : a
greater stratigraphic range for that species than has been hitherto supposed : or a
Lower Carboniferous age for the Louisiana Limestone. Without firm evidence in
support of any one interpretation, it seems preferable to assign the present specimens
to 5. anteposicornis Scott.

One feature of the stratigraphically older specimens of this species (PI. 3, fig. 6a), is
the prominent square antero-aboral angle of the blade, and the posterior inclination
of the three large anterior denticles. These features, though present, are less marked
in stratigraphically younger specimens (e.g. PI. 3, fig. 7a). There also seems to be an

BRITISH AVONIAN CONODONT FAUNAS

223

anterior migration of the lateral denticle in stratigraphically younger specimens in
the present faunules, but the samples are too small to justify any firm conclusion.

Spathognathodus bischoffi sp. nov.
Plate 4, figs. ia-4c

1956 Spathognathodus costatus (E. R. Branson) Bischoff & Ziegler : 166, PI. 13, fig. 3.

J 957 Spathognathodus costatus (E. R. Branson) Bischoff : 56, PL 4, fig. 28.

J 957 Spathognathodus costatus (E. R. Branson) Ziegler in Fliigel & Ziegler ; PI. 1, figs. 15, 18

only.
*959 Spathognathodus costatus (E. R. Branson) Helms : PL 111, figs. 2-4.
J 959 Spathognathodus costatus (E. R. Branson) Voges : 297, text-fig. 5, fig. 1.
1962 Spathognathodus costatus costatus (E. R. Branson) Ziegler : 107, 108, PL 14, figs. 1-6,

8-10.

Derivation of name. In honour of Dr. G. Bischoff.

Diagnosis. Elongate spathognathodid with, a greatly laterally expanded
pseudopolygnathid-type basal cavity, a central oral blade of very uniform, confluent,
blunted denticles, and a series of about twelve strong, low, regular, laterally-elongate
nodes developed along whole inner length of unit except for anterior blade. Outer
oral surface of cup may be feebly nodose.

Material. 10 specimens : Holotype X 401, Paratypes (all figured) X 398, X 400,
X399-

Type locality and horizon. Honnetal, West Germany to VI Zone-Upper
costatus Zone, Roadside cutting (Ziegler 1962).

Description. These elongate spathognathodids have an anterior blade two to
three times as deep as the posterior end of unit. The anterior blade consists of about
3 to 4 confluent, but apically discrete denticles, their apices being bluntly pointed.
The anterior edge is straight and deep, making an angle of 80 "-90° with the aboral

Lateral denticles

Orol edge

Posterior edge

Posterior portion of blade

Anterior denticle

____— -Anterior edge
Antero-aborol angle

Anterior portion o(
blade

Aboral edge
/ Basal cavity

Cavity lips
Fig. 46. Spathognathodus sp. showing morphological terms used in the text.

224 BRITISH AVONIAN CONODONT FAUNAS

edge, the antero-aboral angle being bluntly rounded to angular and conspicuous.
The median denticles, posterior to the blade, are confluent for their whole length,
their individual tips being only rarely discernible. Those in the median two-thirds
of the unit are of uniform height, the posterior ones being shorter, and having 4 to 6
conspicuous apices.

The basal cavity is longitudinally restricted but makes a conspicuous feature in
lateral view.

In oral view, the blade is seen to be gently curved in a horizontal plane, although
only left forms are known. The denticles are conspicuously laterally expanded to
give a platform-like appearance to the whole unit. The size of the platform increases
during ontogeny (cf. PI. 4, figs, ia & 4a). There are up to 14 transverse denticles
developed, those near mid-length being the widest, giving the platform a general
biconvex outline in oral view. Deep transverse troughs separate the denticles, and
there is a tendency for a feeble longitudinal trough to develop also.

In aboral view the asymmetrical laterally expanded basal cavity is a conspicuous
feature, both its lateral expansion and its asymmetry increasing in ontogeny. Its
transverse axis lies obliquely to the longitudinal axis of the unit, the outer (convex)
extension pointing more posteriorly. It extends to the posterior end of the unit as a
deep and wide but gradually narrowing cavity, and as a slit-like groove along the
anterior part of the blade.

Spathognathodus coaptus (Branson & Mehl)
Plate 7, figs, ga-nc

1934 Spathodus coaptus Branson & Mehl : 275, PI. 22, fig. 16.

1938 Spathodus elongatus Branson & Mehl (partini) : 139, PI. 23, fig. 6 only.

1939 Spathodus crassidentatus Branson & Mehl ; Cooper : 413, PI. 45, fig. 19.
1939 Spathodus aciedentatus E. R. Branson ; Cooper : 413, PI. 45, figs. 26, 28, 44.
x 939 Spathodus chouteauensis Cooper : 413, PI. 45, fig. 20.

1939 Spathodus isus Cooper : 413, PI. 45, fig. 33.

1939 Spathodus strigilis Huddle ; Cooper : 416, PI. 45, fig. 37.

1939 Spathodus sulciferus Branson & Mehl ; Cooper : 416, PI. 45, figs. 17, 18.

1949 Spathognathodus sulciferus (Branson & Mehl) Youngquist & Patterson : 72, PI. 15, fig. 1.

1949 Spathognathodus crassidentatus (Branson & Mehl) Youngquist & Patterson : 71, PI. 15,

fig. 2.

1949 Spathognathodus aciedentatus (E. R. Branson) Youngquist & Patterson : 17, PI. 15,

fig- 3-
? 1949 Spathognathodus aciedentatus (E. R. Branson) Thomas : 412, PI. 4, fig. 7.
1951 Spathognathodus macer (Branson & Mehl) Youngquist & Downs : 791, PI. 3, figs.

1, 2.
1958 Spathognathodus crassidentatus Branson & Mehl ; Freyer : 85, PI. 6, fig. 138.
1964 Spathognathodus crassidentatus Branson & Mehl ; Rexroad & Scott : 48, PI. 3, figs.

7.8.

Material. 68 specimens : figured, X 453, X 454, X 436.

Range. Avon Gorge Z i-Z 38.

Description. This is a straight bladed spathognathodid, with a straight aboral

BRITISH AVONIAN CONODONT FAUNAS 225

edge. The 3 or 4 anterior denticles are higher than those of the rest of the blade.
The number of oral denticles is variable but averages 15. The denticles of the oral
edge are of uniform elevation with the exception of the posterior two or three, which
may be slightly lower. The basal cavity is situated at the mid-length of the unit and
is circular in outline.

The denticles of the oral edge are of fairly uniform elevation, with the exception of
those at the posterior tip, which are slightly lower, and those at the anterior, which
rise gradually to form an anterior blade. The anterior and posterior edges are
straight, and form right angles with the aboral edge. The aboral edge is straight.
The basal cavity is sub-circular in outline and centrally situated.

Remarks. Spathognathodus coaptus closely resembles 5. crassidentatus and S.
denticulatus. In S. crassidentatus the aboral edge is arched in the posterior two
thirds. In S. denticulatus the basal cavity is narrow and elongate.

Spathognathodus costatus costatus (E. R. Branson)

Plate 3, figs. I3a-i5b

1934 Spathodus costatus E. R. Branson : 303, PI. 27, fig. 13.

1938 Spathodus costatus E. R. Branson ; Branson & Mehl : 132, 136, PI. 33, fig. 1.
1944 Spathodus costatus E. R. Branson ; E. B. Branson : 181, PI. 32, fig. 1.
? 1949 Spathognathodus costatus (E. R. Branson) Thomas : 409, 412, PI. 4, fig. 10.
non 1956 Spathognathodus costatus (E. R. Branson) Bischoff & Ziegler : 166, PI. 13, fig. 3.
non 1957 Spathognathodus costatus (E. R. Branson) Bischoff : 56, PI. 4, fig. 28.
non 1957 Spathognathodus costatus (E. R. Branson) ; Ziegler in Fliigel & Ziegler : PI. 1,

figs. 15, 18 only.
non 1959 Spathognathodus costatus (E. R. Branson) Helms : PI. in, figs. 2-4.
non 1959 Spathognathodus costatus (E. R. Branson) Voges : 297, text-fig. 5, fig. 1.
non 1959 Spathognathodus cf. costatus (E. R. Branson) Voges : 297, PI. 34.
non 1962 Spathognathodus costatus costatus (E. R. Branson) Ziegler : 107, 108, PI. 14, figs. 1-6,
8-10.
? 1964 Spathognathodus costatus costatus (E. R. Branson) Higgins, Wagner-Gentis &
Wagner : PI. 5, fig. 21.

Material. 170 specimens : figured, X 455, X 166, X 456.

Range. North Crop ZLA 2-ZL 10, Avon Gorge K 18-Z 28.

Description. The unit is slightly arched and bowed, being highest at the anterior
end, although the anterior blade is only about one third as high again as the posterior
end. The oral profile is sigmoidal, the anterior blade being highest and consisting of
3 or 4 large denticles, the tallest of which is either the anterior-most or penultimate
anterior denticle. The denticles of the mid-region are of equal height, and lower than
the anterior denticles, and the unit shallows posteriorly. Situated on the inner side
of the unit is a row of peg-like nodes, 5 to 8 in number, which tend to jut out of the
unit. These nodes may be joined to the main unit by transverse ridges, but these
ridges lie below the level of the node tips.

In aboral view the cavity occurs in mid-length, is fairly large and symmetrical, and
is widest at its mid-point. It extends as a narrow groove to near the posterior
termination and for a short distance along the anterior blade.

226 BRITISH AVONIAN CONODONT FAUNAS

Spathognathodus costatus sulciferus (Branson & Mehl)
Plate 3, figs. i6a-i8c

1934 Spathodus sulciferus Branson & Mehl : 274, PI. 22, figs. 12, 13.
1934 Spathodus spinulicostatus E. R. Branson : 305, PI. 27, fig. 19.
1938 Spathodus spinulicostatus E. R. Branson ; Branson & Mehl : 132, PI. 33, fig. 2.
non 1939 Spathodus sulciferus Branson & Mehl ; Cooper : 416, PL 45, figs. 17, 18 (fig. 17 = S.

cyrius, fig. 18 = S. crassidentatus).
1944 Spathodus spinulicostatus E. R. Branson ; E. B. Branson PL 32, fig. 2.
1944 Spathognathodus sulciferus (Branson & Mehl) Branson & Mehl in Shinier & Shrock :

PL 94, fig. 2.
? 1961 Spathognathodus costatus spinulicostatus (E. R. Branson) Higgins, Wagner-Gentis &

Wagner : PL 5, fig. 22.

Material. 29 specimens : figured, X 457, X 458, X 459.

Range. North Crop ZLA 4-ZL 10, Avon Gorge K 18-Z 26.

Description. The unit is straight, very slightly arched and highest at the
anterior end. The anterior blade consists of 3 to 4 high denticles, its oral outline
being gently convex upward. The medial part of the unit possesses denticles of
equal height, the posterior part having denticles which become progressively lower
toward the posterior termination. Both lateral faces of the unit bear nodes, the
inner row of about 10 being similar to the inner row of S. costatus costatus, with the
largest nodes lying in the medial position and having depressed and inconspicuous
transverse connecting ridges. The outer lateral dentition is confined mainly to the
area of the oral side of the cavity lip and consists of 1 to 3 large fused nodes of lower
height than the inner row. The posterior part of the outer face occasionally bears
isolated denticles (PI. 3, fig. 16).

In aboral view the cavity is large, medial and sub-symmetrical, tending to have a
greater amount of flaring on the outer side ; it is about twice as long as wide and runs
posteriorly as a narrow groove. It is laterally expanded, and wider at the anterior
end.

Remarks. S. costatus sulciferus is obviously very closely related to 5. costatus
costatus, differing only in the addition of lateral denticles on the outer side. Further
enlargement of the outer platform gives species referable to the genus Pseudopoly-
gnathus, although that genus is polyphyletic.

Spathognathodus crassidentatus (Branson & Mehl)
Plate 3, figs. ia~4b

1934 Spathodus crassidentatus Branson & Mehl : 276, PL 22, figs. 17, 18.

1934 Spathodus crassidentatus Branson & Mehl ; E. R. Branson : 303, PL 27, fig. 12.

1934 Spathodus denticulatus E. R. Branson : 305, PL 27, fig. 17.

1934 Spathodus aciedentatus E. R. Branson : 306, PL 27, figs. 21, 23.

1934 Spathodus strigilis Huddle : 89, PL 7, fig. 15 ; PL 12, fig. 11.

1934 Spathodus parvus Huddle : 90, PL 7, fig. 16.

1938 Spathodus crassidentatus Branson & Mehl ; Branson & Mehl : 132, 137, PL 33, fig. 5.

1938 Spathodus elongatus Branson & Mehl (partim) : 139, PL 34, fig. 9 (non PL 34, fig. 6 = 5.
elongatus) .

BRITISH AVONIAN CONODONT FAUNAS 227

!939 Spathodus crassidentatus Branson & Mehl ; Cooper : 413, PI. 45, fig. 19.

J 939 Spathodus aciedentatus E. R. Branson ; Cooper : 413, PI. 45, figs. 26, 28, 44.

T 939 Spathodus chouteauensis Cooper : 413, PI. 45, fig. 20.

T 939 Spathodus strigilis Huddle ; Cooper : 416, PI. 45, fig. 37.

J 939 Spathodus sulciferus Branson & Mehl ; Cooper (partim) : 416, 420, PI. 45, fig. 18.

*939 Spathodus isus Cooper : 413, PI. 45, fig. 33.

1943 Spathodus strigilis Huddle ; Cooper & Sloss : 175, PI. 28, figs. 3, 4, 10, 12.

1943 Spathognathodus crassidentatus (Branson & Mehl) Cooper & Sloss : 175, PI. 28, fig. 1.

1949 Spathognathodus crassidentatus (Branson & Mehl) Youngquist & Patterson : 71, PI. 15,

fig. 2.

1949 Spathognathodus aciedentatus (E. R. Branson) Youngquist & Patterson : 71, PI. 15, fig. 3.

1949 Spathognathodus quintidentatus Thomas : 429, PI. 4, figs. 8, 9.

1949 Spathognathodus aciedentatus (E. R. Branson) Thomas, PL 4, fig. 7.

1956 Spathognathodus crassidentatus (Branson & Mehl) Bischoff & Ziegler (partim) : 166,
PI. 13, fig. 14 (non PI. 13, fig. 13).

z 957 Spathognathodus crassidentatus (Branson & Mehl) Bischoff : 56.

1961 Spathognathodus crassidentatus (Branson & Mehl) Freyer : 85, PI. 6, fig. 138.

1964 Spathognathodus crassidentatus (Branson & Mehl) Rexroad & Scott : 48, PI. 3, figs. 7,
8.

Material. 222 specimens : figured, X 460, X 461, X 462, X 463.
Range. North Crop KL 2-ZLA 33, Avon Gorge K 17-Z 38.

Description. This is a simple arched and bowed unit, which is highest at the
anterior. The anterior blade consists of 3 to 6 tall, massive denticles which are
basally confluent, with discrete blunt apices, the denticles in the medial part of the
blade being highest. The mid-third of the unit consists of denticles of even height,
conspicuously lower than the anterior denticles. The denticles of the posterior third
decrease in height towards the posterior termination. The total number of denticles
ranges from 17 to 22.

In aboral view a large cavity, situated medially, is symmetrically flared and widest
just anterior to its mid-point. The cavity is extended both anteriorly and posteriorly
as a narrowing groove, the posterior extension being the longer.

Remarks. This species is common, and, as was pointed out by Rexroad and Scott
(1964 : 49), is highly variable. Although we accept most of the synonomy of those
authors, we believe that forms with a very much greater denticle density should not
be included under S. crassidentatus, but should be referred to S. cyrius (Cooper) (see

P- 234)-

Spathognathodus cristulus Youngquist & Miller

Plate 8, figs. I4a-i8d

1949 Spathognathodus cristula Youngquist & Miller : 621, PI. 101, figs. 1-3.

1957 Spathognathodus cristula Youngquist & Miller ; Rexroad : 38, PI. 3, figs. 16, 17.

1958 Spathognathodus cristula Youngquist & Miller ; Rexroad : 25, PI. 6, figs. 3, 4.

T961 Spathognathodus cristula Youngquist & Miller ; Rexroad & Burton : 1156, PI. 141,
fig. 9-

1962 Spathognathodus cristula Youngquist & Miller ; Rexroad & Liebe : 511, table 1.

1964 Spathognathodus cristula Youngquist & Miller ; Rexroad & Furnish : 674, PI. 111,

fig- 15-

1965 Spathognathodus cristula Youngquist & Miller ; Rexroad & Nicoll : 26, PI. 1, figs. 1, 2.

228 BRITISH AVONIAN CONODONT FAUNAS

Material. 278 specimens : figured, X 464, X 465, X 466, X 467, X 468.
Range. North Crop CYD 7, Avon Gorge Z i-D 26.

Description. This spathognathodid bears 8 to 12 denticles along its oral edge,
of which the most anterior is the largest. The remaining denticles decrease uni-
formly in size towards the posterior end, so that the general form of the denticulate
edge is continuously convex, being lowest posteriorly. The basal cavity extends for
about two-thirds the length of the unit. It is widest at the anterior end, and is
continuous to the posterior end, being biconvex in outline.

The short blade is distinguished by a deep anterior end, with a high anterior
denticle. The anterior edge of the unit slopes conspicuously forward so that its
antero-aboral projection lies in front at the tip of the denticle. The antero-aboral
angle is either bluntly rounded or more or less angular, forming an angle of about 90 °.
The anterior edge is straight. The anterior denticle is about half as long again as
that adjacent to it, and about twice as wide. The remaining denticles of the bar
decrease uniformly in size towards the posterior end. Except for the two posterior
denticles which tend to be conspicuously smaller than the rest, the denticles are
discrete only at their bluntly rounded tips. They have convex lateral faces and
stand erect to the bar. The posterior margin, which is formed of the two most
posterior denticles, tends to slope posteriorly. In lateral view the aboral edge of the
unit is straight in the anterior third of the unit, but is concave posteriorly, because
of the flare of the basal cavity. This cavity is slightly asymmetrical, but is strongly
convex in outline and extends for about two thirds the length of the aboral surface.
Its maximum width is only about half or a third of its total length and its greatest
depth and width are anterior. It extends anteriorly as a median slit along the
anterior blade.

There is a tendency in some specimens for the posterior denticles to be progressively
posteriorly inclined towards the posterior end. In some specimens the anterior
aboral angle is rather less than 90 ° and the apical denticle is more sharply triangular
in lateral view than in other specimens.

Remarks. The first stratigraphic occurrence of Spathognathodus cristulus in the
Avonian of the Bristol area is considerably older than that known in other parts of
the world.

Spathognathodus elongatus (Branson & Mehl)
Plate 7, figs. ia-5b

1938 Spathodus elongatus Branson & Mehl : 139, PI. 34, fig. 6 {-non PI. 34, fig. 9 = S. crassi-

dentalusl) .
1944 Spathodus elongatus Branson & Mehl ; E. B. Branson : PI. 39, fig. 6, (non PI. 39, fig.

9 = S. crassidentatus?).

Material. 48 specimens : figured, X 472, X 473, X 474, X 475.

Range. North Crop KL 19-ZL 8, Avon Gorge K 4-Z 13.

Description. The blade is straight or gently curved in oral view, being long and

BRITISH AVONIAN CONODONT FAUNAS 229

shallow over the whole length. The denticles are highest at the anterior end,
decreasing in height towards the position of the anterior end of the cavity, beyond
which they increase in size towards the posterior end of the cavity, and then decrease
gradually towards the posterior end of the unit. The denticles are compressed, fused
at their bases, and free at their tips ; about 20 in number. Longitudinal
' shoulders ' are developed on the lateral faces below the bases of the denticles. The
aboral outline is straight to slightly arched. The very shallow depth of the blade
just anterior to the basal cavity gives a ' sagging ' profile to the unit. The length
of the unit is about four times the maximum depth.

The cavity is symmetrical, elongate and shallow, with a slight appearance of cups.
It narrows to grooves at both ends, which extend about halfway along aboral edges
towards anterior and posterior ends.

Remarks. Our specimens agree perfectly with the figured holotype of S. elongatus
(Branson & Mehl, 1938A, PL 34, fig. 6), although their description is scarcely adequate
to distinguish this from other species. Within our fauna there appear to be two
forms ; the first includes those with free standing fine denticles (PL 7, fig. 5a) which
tend to be sharper, longer and of more regular length than those of the second group,
which have laterally compressed denticles (PL 7, fig. ia). The long, free-standing
denticles of this first group are reminiscent of S. denticulatus (E. R. Branson) (1934,
PL 27, fig. 17), but the differences in relative length of the units and anterior dentition
preclude us from placing these forms within that species. Cooper (1939 : 413) refers
the paratype (PL 34, fig. 9) to a new species S. chouteauensis. Rexroad & Scott
(1964 : 48) refer both the holotype and paratype to S. crassidentatus (Branson &
Mehl). It is possible that the paratype, referred to S. chouteauensis by Cooper, is
referable to S. crassidentatus (Branson & Mehl) but the holotype is definitely a
separate species.

Spathognathodus plumulus plumulus sp. et subsp. nov.
Plate 1, figs. ia-2c, 5, 6

Derivation of name. From the plume-like anterior blade.

Diagnosis. Spathognathodid with plume-like anterior blade, denticles of which
decrease rapidly in size anteriorly from a massive denticle at posterior end of blade.
Series of lateral nodes present, developed on the outer side only, above the basal
cavity.

Material. 442 specimens : Holotype X 476, Paratypes X 379, X 380, X 381
(all figured).

Type locality and horizon. R. Clydach, Nr. Gilwern, K Zone North Crop.
Sample KL 4.

Range. North Crop KL i-KL 16, Avon Gorge K 2-K2 1.

Description. The blade is plume-like in anterior third, consisting of 3 to 6
denticles, decreasing rapidly in height anteriorly from a tall massive denticle situated
immediately anterior to the basal cavity. The remainder of the unit is low, consist-

230 BRITISH AVONIAN CONODONT FAUNAS

ing of about 16 fused, laterally compressed denticles, those in the posterior third of
the unit tending to be the largest. The oral profile, posterior to the blade, is gently
convex. Lateral denticles are developed on the outer side above the basal cavity
and number from 2 to 5 ; they tend to form a short platform, restricted to the region
of the basal cavity, rather than occurring as laterally divergent peg-like denticles.
The aboral lateral profile is conspicuously straight, being arched behind the cavity.

In aboral view the cavity is ovate, slightly asymmetrical, the flared side being the
narrower. The long axis is parallel to the long axis of the unit, equal to, or only
slightly greater than, the maximum lateral width of the cavity. The cavity may
extend as a faint groove for a short distance along the anterior and posterior blades.

Remarks. Ziegler (1960A, PI. 3, figs. 8, 9) described forms referred by him to 5.
tridentatus, which appear to be referable to S. plumulus plumulus. The form figured
by him (i960 A, PI. 3, fig. 7) as S. sulci jer us is distinct from Branson & Mehl's type
specimen which is, in fact, a senior synonym of S. spinulicostatus (E. R. Branson
1934). Ziegler's specimen appears from its tall blade and the nature of the anterior
face to be closely related to S. plumulus plumulus, but its lack of platform develop-
ment precludes its inclusion in that species, although it may be a form ancestral to
spathognathodids with high plume-like blades.

S. plumulus plumulus is probably ancestral to Clydagnathus (see p. 85). The
lateral profile of the blade, with its sharply descending oral surface, short anterior
edge, and rounded antero-aboral angle, is also very similar to that of Scaphignathus.

Spathognathodus plumulus nodosus sp. et subsp. nov.
Plate 1, figs. 3a~4C

Derivation of name. From the additional nodes on the inner side of cup.

Diagnosis. Subspecies of S. plumulus with one or more nodes developed on inner
platform expansion.

Material. 14 specimens : Holotype X 382, Paratype X 383.

Type locality and horizon. R. Clydach, Nr. Gilwern, Lower K Zone North
Crop. Sample KL 2.

Range. North Crop KL i-KL 6, Avon Gorge K-8.

Description. This form is similar to S. plumulus plumulus in gross morpho-
logical detail, but the inner oral lip of the expanded cavity bears one or more nodes.

Remarks. As in the S. tridentatus group, the S. plumulus group develops lateral
denticles on the inner and outer lateral margins of the cup. In 5. plumulus nodosus
the development towards a pseudopolygnathid morphology (as in the S. aculeatus
and S. tridentatus groups) is seen. The development of the denticle ranges from
weak to strong.

Spathognathodus plumulus shirleyae subsp. nov.
Plate 1, figs. 7a-8c

Derivation of name. After Mrs. Shirley Osborn.

BRITISH AVONIAN CONODONT FAUNAS 231

Diagnosis. Spathognathodid with plume-like anterior blade, having one node
developed on outer lateral face above basal cavity.

Material, io specimens : Holotype X 384, Paratype X 385 (both figured).

Type locality and horizon. R. Clydach, Nr. Gilwern, Lower K Zone North
Crop. Sample KL 2.

Range. North Crop KL 2-KL 3, Avon Gorge K 4-K 8.

Description. The blade is short and thin, the anterior part consisting of a
posterior high, massive, recurved, laterally compressed denticle, and the denticles
rapidly decreasing in height anteriorly, to give a plume-like effect. The medial and
posterior parts of the unit consist of low, fused, laterally compressed, erect to slightly
posteriorly inclined denticles. Above the anterior part of the outer cavity lip, a
single lateral node denticle arises, which is sub-circular in cross-section.

In aboral view the cavity is elliptical, slightly flared and its long axis is concordant
with the long axis of the unit.

Remarks. This form appears to occupy the same position within the S. plumulus
lineage as does S. anteposicornis Rexroad & Scott within the 5. tridentatus lineage.
The small size of all the present specimens might be interpreted to mean that they
are a growth stage of S. plumulus plumulus sp. nov., but the presence of three
denticles in specimens of that species of comparable small size (PI. 1, fig. 6) and the
restricted range of the present subspecies appear to justify its recognition as distinct.

Spathognathodus pulcher (Branson & Mehl)
Plate 4, figs. 9a-nc
1938 Spathodus pulcher Branson & Mehl : 139, PI. 34, figs. 7, 8.

Material. 59 specimens : figured, X 386, X 512, X 513.

Range. North Crop KL 19-ZLA 15, Avon Gorge Z 12-C 7.

Description. The blade is long and thin, being highest at the anterior and
decreasing gradually to a point anterior to the basal cavity, where the profile becomes
straight, sloping off abruptly at the posterior termination. The 14 to 15 sub-circular
denticles are erect, short, fused at the bases, and free at the sharply pointed tips.
The cavity is elongate, expanded, and occurs in the posterior half of the unit,
terminating immediately anterior to the posterior end. The anterior part of the
blade is about twice as deep as the posterior.

Remarks. This form differs from S. crassidentatus s.s., in the lack of a distinct
high blade at the anterior end, and in the posterior (rather than medial) position of
the basal cavity. It resembles S. elongatus in the anterior half, but the sudden
termination immediately posterior to the basal cavity is distinctive (Branson & Mehl
1938A : 139-140, PI. 34, figs. 7, 8). It is very similar to a form described by Branson
& Mehl (1938A) asS. elongatus (PL 34, fig. 9) which was referred by Cooper (1939) to a
new species, S. chouteauensis. Rexroad & Scott (1964) refer this to S. crassidentatus,
but it would appear not to fit even their broad terms for the species. The present
specimens are also close to S. stabilis.

232 BRITISH AVONIAN CONODONT FAUNAS

Spathognathodus scitulus (Hinde)
Plate 8, figs. 9a-nd

1900 Polygnathus scitulus Hinde : 343, PI. 9, figs. 9-1 1 only.

1928 Panderodella scitula (Hinde) Holmes : 16, PI. 6, figs. 26, 28 only.

i960 Spathognathodus scitulus (Hinde) Clarke : 21, PI. 3, figs. 12, 13.

1962 Spathognathodus scitulus (Hinde) Rexroad & Collinson : 20, PI. 2, figs. 14, 19, 29-31.

Material. 19 specimens : figured, X 391, X 392, X 393.
Range. North Crop CYD 6-3D 14/15, Avon Gorge C 15-D 27.

Description. This spathognathodid is characterized by having an oral outline
that is straight in the mid-third, but which plunges steeply towards the posterior end.
It has relatively few denticles on the oral edge and a widely flared, arched, basal
cavity on the outer lateral face. The posterior end is shallow and pointed.

This short spathognathodid has a prominent plough-like antero-aboral area which
may sometimes develop an irregular anterior edge. The antero-aboral margin is
acute and more or less pointed and its posterior edge is feebly convex. The anterior
edge of the unit is generally straight. The oral edge bears 9 denticles, which stand
more or less erect to the general line of the blade, only their apices being discrete.

The denticles decrease regularly in size towards the posterior end of the unit, the
posterior 2 or 3 tending to be minute in size. The anterior denticle is much the
largest, but the subsequent 4 or 5 denticles tend to be of rather uniform size, and the
mid-third of the unit has a rather straight lateral edge. In outer lateral view, the
sharp flexure of the unit and the widely flared basal cavity are prominent features.
The posterior end of the unit is very shallow. The aboral edge is continuously
concave and the posterior edge is bluntly pointed. The basal cavity itself is confined
to the mid- third of the unit and it is flared only on the outer lateral side, the inner
side being straight.

Spathognathodus scitulus subsp. nov. A
Plate 31, figs. I2a-c

Material. 3 specimens : X 390 (figured).
Range. Scotland DUN 78.

Description. A Spathognathodus scitulus with one or two inconspicuous
accessory denticles developed on the anterior edge of the main denticle.

The present specimens agree with typical individuals of 5. scitulus (e.g. those
illustrated by Rexroad & Collinson 1963, and Clarke i960) except that the " cusp "
(the most anterior denticle of the blade) has two small confluent denticles on its
anterior aboral edge, which are developed parallel to the anterior margin. The
denticles posterior to the main denticle, the general form of the blade, and the
general structure and asymmetry of the basal cavity are otherwise similar to those
of Spathognathodus scitulus s.s.

BRITISH AVONIAN CONODONT FAUNAS 233

Spathognathodus cf. catnpbelli Rexroad
Plate 8, figs. ia-4c

1957 Spathognathodus campbelli Rexroad : 37, PI. 3, figs. 13-15.
i960 Spathognathodus pusillus Clarke : 20-21, PI. 3, figs. 10, 11.
1965 Spathognathodus cf. campbelli Rexroad ; Rexroad & Nicoll : 26, PI. 1, fig. 6.

Material, ii specimens : figured, X 450, X 451, X 452, X 435.

Range. North Crop CYD 6-3D 19.

Description. The most distinctive features of the present specimens are the
deep and relatively short blade, which is almost as deep as the longest oral denticles ;
the series of up to 20 laterally compressed denticles of which the largest occurs at
about mid-length ; the marked flaring of the basal cavity, which is confined to the
posterior half of the unit ; and the gentle posterior deflection in a vertical plane of
the posterior half of the unit. In lateral view the oral margin is sharply denticulated,
tending to be straight and rather sloping in the anterior half, and more or less convex
in the posterior half. There are 17 to 20 denticles on the oral edge of the blade.
These show a rough increase in size from the anterior denticle to the denticle at about
mid-length of the blade, which is the largest of the whole blade and is feebly inclined
posteriorly to the basal surface of the blade. The other denticles of the anterior part
of the blade are more or less erect and are confluent for most of their length, although
their apical portions are discrete and pointed. The denticles of the posterior part of
the blade are all inclined posteriorly. They are discrete for a greater part of their
length than those of the anterior part of the blade, and the degree of posterior
inclination tends to increase towards the posterior end of the blade. Those in the
posterior quarter of the blade tend to be the smallest. The posterior blade decreases
in depth posteriorly and the posterior end is shallow and bluntly spatulate. It is
also conspicuously depressed in a vertical plane towards the posterior end. The
other striking feature in lateral view is the widely flaring and elongate basal cavity,
the anterior end of which is aligned with the anterior edge of the largest denticle.

In aboral view the cavity has a strongly biconvex outline and is extended virtually
to the posterior end of the blade. It is continued anteriorly to the anterior edge of
the main denticle as a very inconspicuous and narrow slit.

Remarks. The present specimens differ somewhat from those described by
Rexroad in having a rather conspicuously developed denticle at about mid-length.
In other respects the specimens are closely similar, especially in the general form of
the basal cavity, which tends to be more rounded anteriorly than it is posteriorly, and
to have its deepest point near the anterior end. The longitudinal line immediately
above the level of the navel, which marks the thin basal edges of the unit, is well seen
under certain conditions of lighting.

Spathognathodus cf. cristulus Youngquist & Miller
Plate 8, figs. 7a-8c, I2a-i3b

1938 Spathognathodus regularis Branson & Mehl (partim) : 137, PI. 34, fig. 2 only (non PI. 34,
figs. 1, 3, 10 = S. regularis).

j.U BRITISH .WOMAN CONODONT FAUNAS

Material. 387 specimens : figured, X 554-X 557.

Range. North Crop ZLA 2-ZLA 33, Avon Gorge Z 35-D 27.

Description. This species is a simple denticulate unit bearing a regular succes-
sion of denticles which decrease in height from anterior to posterior. The anterior
denticle tends to be massive, taller and nearly twice as wide as the remainder ; the
next two denticles in a posterior direction tend to be fairly narrow and fused ; the
remainder have free chevron-shaped tips and are slightly larger.

In aboral view the cavity is large with some flaring of the lips ; it begins imme-
diately posterior to the anterior denticle and runs to the posterior termination of the
unit. The lips are arched anteriorly and the whole cavity is symmetrical.

Remarks. This form agrees very closely with S. cristulus (Youngquist & Miller,
1949 : 621, PI. 101, figs. 1-3), except that their specimens commonly have 10 smaller
denticles, whereas the present forms have from 7 to 16 denticles. They agree
exactly with a form included in S. regularis (Branson & Mehl 1938 A), even to the
number of denticles. Branson & Mehl, and Rexroad & Scott (1964 : 50) recognize
forms with one major anterior denticle within the specific terms of S. regularis, but
since our fauna contains specimens with only one major denticle, and no specimens
with the two anterior denticles typical of the holotype of S. regularis, there are
obviously two separate species involved. The present specimens are compared to
S. cristulus because of their close resemblance, but they are stratigraphically younger
and may be a separate, perhaps ancestral, species.

Spathognathodus cf. cyrius (Cooper)
Plate 7, figs. I2a-i4c

1939 Spathodus sulciferus Branson & Mehl ; Cooper (partim) : PI. 45, fig. 17, (non PI.

45, fig. 18 = 5. cvassidentatus) .
!939 Spathodus cyrius Cooper : 413, PI. 45, fig. 25.
non 1943 Spathognathodus cyrius (Cooper) Cooper & Sloss : 175, PI. 28, figs. 3, 4, 10, 12

(=5. crassidentatus) .
1951 Spathognathodus macer Branson & Mehl ; Youngquist & Downs : 791, PI. in,

figs. 1, 2.

Material. 19 specimens : figured, X 470, X 469, X 471.
Range. North Crop KL 2-ZLA 2, Avon Gorge Z i-Z 13.

Description. This is a simple arched and bowed unit which is highest at the
anterior end ; the anterior part consists of 3 high denticles with the medial one the
largest. The rest of the unit is made up of lower denticles, the medial part consisting
of denticles of equal height and the posterior part shallowing with progressively
smaller denticles. In the medial part the denticles are very fine and fused, 2 denticles
commonly having only one emergent oral extremity. The unit commonly bears,
besides the large anterior denticles, 30 smaller denticles.

The cavity is situated medially and is relatively small and pear-shaped.

BRITISH AVONIAN CONODONT FAUNAS 235

Remarks. This species bears a marked resemblance to S. crassidentatus and was
included in that species by Rexroad & Scott (1964), but the very different dentition
serves to distinguish it. The medial and posterior oral parts commonly bear 30
denticles, as opposed to the 15 or so of S. crassidentatus. Between the anterior part
of the cavity and the anterior high blade, this species has 7 to 8 denticles whereas S.
crassidentatus has only 2 to 3. Cooper's holotype has a total of only 20 denticles, but
is otherwise very similar to the present specimens. The present specimens also
resemble those described by Cooper (1939, PI. 45, fig. 17 only) as Spathodus sulciferus
Branson & Mehl (fig. 18 of Cooper's PI. 45 is probably 5. crassidentatus) and those
described as S. macer by Youngquist & Downs (1951, PI. in, figs. 1, 2). S. chou-
teauensis Cooper (1939, PI. 45, fig. 20) is also broadly similar and also has resem-
blances to S. crassidentatus.

Spathognathodus cf. robustus (Branson & Mehl)
Plate 7, figs. 6a-7c

1934 Spathodus robustus Branson & Mehl : 189, PI. 17, fig. 21.

Material. 17 specimens : figured, X 387, X 388.
Range. North Crop KL 19-ZLA 14, Avon Gorge K2 1.

Description. The unit is bar-like, being highest at the anterior end and sloping
towards the posterior end, the oral outline being nearly straight. The anterior
denticles tend to be massive. Smaller denticles appear on the anterior edge of the
anteriormost massive denticle, giving a posteriorly inclined anterior edge which
makes a sharp angle of about 60 °, with the aboral edge. The denticles in the median
part of the unit are fused, two denticles often fusing into one free tip. The posterior
bar-like part of the unit is shallow, twisted and depressed downwards, the denticles
tending to be isolated and free standing and curved towards the inner side.

In aboral view the cavity is fairly large, elongate, medially situated, about twice as
long as wide, the wider anterior end narrowing rapidly towards the anterior of the
unit and the other end narrowing slowly towards the posterior ; the lips are
thickened slightly.

Remarks. Branson & Mehl (1934, PI. 17, fig. 21) described a form very similar to
ours as S. robustus. The dentition is very similar, except that in their specimen the
massive anterior denticle and the isolated posterior denticles are less conspicuously
developed than those of the present specimens.

There appears to be a morphological trend from these specimens through such
forms as Spathognathodus sp. B. to a pseudopolygnathid form.

The Spathognathodus tridentatus group

Much confusion has arisen in recent conodont literature (Sannemann 1955,
Bischoff & Ziegler 1956, Freyer 1961 and Ziegler 1962) with regard to specimens of
the genus Spathognathodus which develop lateral denticles. Spathognathodids with

236 BRITISH AVONIAN CONODONT FAUNAS

lateral denticles have been described by Branson & Mehl (1933), E. R. Branson
(1934) and Scott (1961), from the Grassy Creek, Bushberg/Hannibal, and Louisiana
Limestone Formations respectively.

German workers recognized a progressive addition of denticles, firstly on the inner
lateral face, and secondly on the outer lateral face. Forms with denticles confined
to the inner supra-cavity position were referred to S. aculeatus (Branson & Mehl),
whereas forms with a development of lateral denticles along the whole length of the
unit, except for the high anterior blade, were referred to subspecies of 5. costatus
(E. R. Branson). Scott (1962 : 1224) separated as a distinct species (S. anteposi-
cornis), forms with a single node immediately anterior to the oral surface of the
cavity.

From studies of the present British conodont faunas it appears that within the
period Upper Devonian (to V) to Lower Carboniferous (Cu II a), there has been
multiple development of laterally nodose spathognathodids. It appears that the
Grassy Creek (to V) form S. aculeatus (Branson & Mehl) was the first species exhibit-
ing this trend. No other to V forms with further development of lateral denticles
on both lateral faces are known. Forms described from Germany and identified as
5. aculeatus by Ziegler (1961) and other authors may be distinct from S. aculeatus
and are probably a new species.

The further developments of this species referred by Ziegler to S. costatus costatus,
S. costatus spinulicostatus and S. costatus ultimus are definitely not representative of
the species S. costatus (E. R. Branson) and 5. spinulicostatus (E. R. Branson), and are
named herein as new species, S. bischoffi sp. nov. and S. ziegleri sp. nov.

S. costatus costatus (E. R. Branson) (= S. costatus of Branson) and S. costatus
sulciferus (Branson & Mehl) (= S. spinulicostatus of E. R. Branson) appear to be
restricted to an upper Cu I-Lower Cu II a range, and can be seen to develop into
forms referable to the genus Pseudopolygnathus. The fact that species of this genus
are found at lower horizons (e.g. the Devonian-Carboniferous boundary) indicates
that the genus Pseudopolygnathus is polyphyletic, the ancestral forms in both cases
probably being nodose spathognathodids, as suggested by Voges (1959).

Forms with from 2 to 4 lateral denticles, occurring with S. costatus (sensu E. R.
Branson) and S. spinulicostatus (sensu E. R. Branson), appear referable to S.
tridentatus (E. R. Branson), as distinct from S. tridentatus (sensu Sannemann,
Bischoff & Ziegler and Freyer), the latter forms being better referred to S. aculeatus
(sensu Ziegler).

In addition to these forms, there occurs at the base of the Lower Carboniferous in
our sections, beneath and with the first occurrence of the genus Siphonodella, a new
species of laterally denticulate Spathognathodus, with a plume-like anterior blade.
Ziegler (i960 A) described as S. tridentatus a form which appears referable to our new
species S. plumulus plumulus. This species also exhibits evolutionary addition of
denticles on the outer lateral cup but, rather than evolving to give species of the
genus Pseudopolygnathus, it alters by lateral shift of the anterior blade into a homoeo-
morphic form of the genus Cavusgnathus, named herein as a new genus Clydagnathus
(P- 85).

BRITISH AVONIAN CONODONT FAUNAS 237

Spathognathodus tridentatus (E. R. Branson)
Plate 3, figs. 9a-i2c

1934 Spathodus sulciferus Branson & Mehl ; E. R. Branson : 304, PL 27, fig. 15 ? 22

(non PL 27, fig. 20 = S. costatus sulciferus).
1934 Spathodus tridentatus E. R. Branson : 307, PL 27, fig. 25.
1934 Spathodus duplidens Huddle : 91, PL 12, figs. 1-4.

1949 Spathognathodus costatus (E. R. Branson) Thomas : 409, 412, PL 4, fig. 10.
1949 Spathognathodus tridentatus (E. R. Branson) Thomas : 412, PL 4, fig. 11.
non 1955 Spathognathodus tridentatus (E. R. Branson) Sannemann : PL 24, fig. 13.
non 1956 Spathognathodus tridentatus (E. R. Branson) Bischoff & Ziegler : p. 167, PL 13,
figs. 1, 2.
? 1956 Spathognathodus aciedentatus (E. R. Branson) Hass PL 2, fig. 26.
? 1957 Spathognathodus aciedentatus (E. R. Branson) Cloud, Barnes & Hass : PL 5,

fig- 7-
? 1959 Spathognathodus aciedentatus (E. R. Branson) Hass : PL 49, fig. 24.
non 1959 Spathognathodus tridentatus (E. R. Branson) Voges : 658, PL 3, fig. 7.
non i960 Spathognathodus tridentatus (E. R. Branson) Dvorak & Freyer : PL 2, figs. 9, 10.
wok 1961 Spathognathodus tridentatus (E. R. Branson) Freyer : 89, PL 6, fig. 150.
non 1961 Spathognathodus tridentatus (E. R. Branson) Remack-Petitot : 261, fig. 4.

Material. 259 specimens : figured, X 394, X 395, X 396, X 397.
Range. North Crop KL 19-ZLA 27, Avon Gorge K 21-Z 24.

Description. The unit is straight to gently arched in the posterior part and
slightly bowed ; it is highest at the anterior. The anterior blade is composed of 3 to
4 high denticles, the highest being the anterior-most 2 or 3 denticles. The median
denticles are of equal height, and the unit shallows posteriorly, the denticles becoming
shorter, less fused, and rather sharper towards the posterior end.

On the inner side there are developed from 2 to 4 lateral denticles, situated above
the cavity. They are peg-like and are not connected to the main blade by transverse
ridges.

In aboral view the basal cavity is large and symmetrically expanded, the widest
part being at or just anterior to the mid-point. The cavity extends in either direc-
tion as a short aboral groove, the posterior groove being longer than the anterior.

Remarks. This is a very common species with a limited range in our faunas. It
is closely related to and occupies an intermediate phylogenetic position between S.
anteposicornis and S. costatus costatus. It is also very close to S. aculeatus, but its
higher stratigraphical position implies a distinct phylogenetic origin. For this
reason it seems undesirable to regard it as a junior synonym of that species. The
similarity between the two forms is, in any case, not exact. S. aculeatus has a more
conspicuously laterally expanded basal cavity. Individuals from stratigraphically
older samples (e.g. PI. 3, figs, na-c) tend to have a smaller number of blade denticles
(9 to 13) behind the anterior blade than those from younger samples (e.g. PI. 3,
figs, ioa-c), which have from 14 to 19 denticles.

238 BRITISH AVONIAN CONODONT FAUNAS

Spathognathodus ziegleri sp. now
Plate 4, figs. 5a-8d

non 1934 Spathodus spinulico status E. R. Branson : 305, PL 27, fig. 19 [= S. sulciferus].

1956 Spathognathodus spinulicostatus (E. R. Branson) Bischoff & Ziegler : 167, PL 13,

fig- 7-

1957 Spathognathodus spinulicostatus spinulicostatus (E. R. Branson) Bischoff : 57, pi.

4. fi g- 27-
1957 Spathognathodus spinulicostatus spinulicostatus (E. R. Branson) Ziegler in Fliigel

& Ziegler : PL 1, fig. 14.
r 959 Spathognathodus spinulicostatus spinulicostatus (E. R. Branson) Helms : PL 3,

figs. 12a, b.
i960 Spathognathodus spinulicostatus spinulicostatus (E. R. Branson) Remack-Petitot :

261, fig. 4.
i960 Spathognathodus spinulicostatus spinulicostatus (E. R. Branson) Dvorak & Freyer :

PL 2, fig. 8.

1961 Spathognathodus spinulicostatus spinulicostatus (E. R. Branson) Freyer : 87, 88, PL 6,
fig. 145, text-fig. 146.

1962 Spathognathodus costatus spinulicostatus (E. R. Branson) Ziegler : 108, PL 14,
figs. 11-18.

1965 Spathognathodus spinulicostatus spinulicostatus (E. R. Branson) Spasov : 102, PL
3. figs- 13. 17-

Derivation of name. This is named in honour of Dr. W. Ziegler.

Diagnosis. Spathognathodus with subdued oral denticulation. Anterior blade
deep, but narrowing posteriorly, oral surface being flat. Strong development of
accessory lateral denticles, up to 13 in number, on outer side of unit. On opposite
side, posterior end of unit also marked by development of up to 7 smaller lateral
denticles, giving whole posterior part an asymmetrical platform-like development.
Basal cavity strongly laterally expanded, but lanceolate in basal outline.

Material. Holotype X 403, Paratypes X 402, X 404, X 437 (all figured).

Type locality and horizon and range. Honnetal, West Germany to VI Zone-
Upper costatus Zone, roadside cutting (Ziegler 1962).

Description. In lateral view the anterior blade is deep but straight, the oral
surface bearing a series of reduced even denticles, only the anterior 3 or 4 of which
have sharply defined apices. There is a tendency for the depth of the anterior blade
to decrease towards the basal cavity, but the oral edge is straight. Behind the basal
cavity there is a marked reduction in depth of the unit as seen in lateral view. The
aboral edge remains more or less straight, but the oral surface slopes down to meet it
in a relatively straight line. Its oral edge makes an angle of about 160 ° with the oral
edge of the blade. The posterior end is spatulate to bluntly-pointed in lateral view.
The basal cavity is a conspicuous feature when seen in lateral view. The oral
posterior surface of the unit bears a series of low irregular denticles developed lateral
to the main blade, but clearly visible in lateral view. These denticles, are developed
on the inner lateral face of the unit. In outer lateral view the unit is broadly
si miliar.

In oral view the most striking feature of the unit is the development of up to 13

BRITISH AVONIAN CONODONT FAUNAS 239

laterally expanded denticles developed on the outer (convex) side of the main blade.
These are barely visible in lateral view, but are conspicuously elongated blunt
denticles in oral view. On the inner (concave) side posterior to the basal cavity, there
is a series of up to 7 broadly similar denticles developed. The two sets of denticles
tend to form a more or less continuous ridge across the posterior platform which they
produce, although in some specimens they are arranged at such an angle to one
another to give an arrow-like oral view. The basal cavity is conspicuously laterally
expanded in oral view, the inner end of its long axis, which lies oblique to the main
axis of the unit, lying anterior to that of the outer side.

In aboral view the cavity is laterally expanded, the greatest width lying near its
anterior end. It is shallow and asymmetrical and tapers more or less uniformly
towards the posterior termination of the unit, having an overall lanceolate lachry-
form outline, the anterior end being rounded.

Remarks. This species differs from S. bischoffi in the development of an accessory
row of posterior lateral denticles. Like that species, no mirror images of forms are
known. In this the two species resemble many species of the genus Pseudopoly-
gnathus, to which both are closely related in their overall morphology.

Spathognathodus sp. A

Plate 4, figs. I2a-c

Material. 4 specimens : figured, X 405.

Range. North Crop KL 3-KL 5.

Description. The unit is arched, relatively short and deep. The major denticles
or pair of denticles occur in the anterior quarter, being massive, tall, and laterally
compressed. The anterior blade occurs anterior to this denticle and is formed of
denticles developed in a fan-like manner on both the oral and anterior faces of the
unit. The median part of the blade is fairly level, but the posterior part decreases in

KrcO*™">%/YM

Fig. 47. The development of Pseudopolygnathus postinodosus from a spathognathodid
ancestor by addition of lateral denticles.

2 4 o BRITISH AVONIAN CONODONT FAUNAS

height rapidly near the posterior termination. The aboral outline of the unit is
arched, the basal cavity being elongate and without flared lips.

Remarks. This species appears to be dissimilar to all other described species of
spathognathodids, although it is closest to 5. crassidentatus.

Spathognathodus sp. B

Plate 7, figs. 8a-c

Material. 4 specimens : figured, X 406.
Range. North Crop ZLA 5, Avon Gorge Z 34-C 7.

Description. The bar is fairly massive being highest anteriorly, with the height
decreasing regularly to the posterior ; the posterior termination is broken. The
anterior-aboral portion of the blade is extended anteriorly as a short flattened
process. The denticles, at least 17 in number, are laterally compressed and fused
over the majority of their length. One lateral denticle occurs immediately anterior
to the anterior margin of the cavity, and reaches the height of the main blade
denticles. The aboral profile of the unit is not straight, the cavity tending to arch
the posterior part upward.

In aboral view the cavity is elongate and moderately flared, extending as a groove
for a short distance posteriorly and anteriorly.

Remarks. This form is probably a pathological variant of 5. cf. robustus, the
lateral dentition placing it in an intermediate position between this and Pseudopoly-
gnathus sp.

Spathognathodus sp. nov.
Plate 6, fig. 9

Material. 15 specimens : figured, X 518.
Locality and horizon. Avon Gorge. Sample Z 19.
Range. Avon Gorge Z 13-Z 19.

Description. A spathognathodid characterized by finely developed oral denticu-
lation on a bar which is deep and protruding antero-aborally, becoming shallower
towards its posterior end. The bar is strongly recurved in its posterior half. The
basal cavity is strongly expanded laterally, and one or more lateral denticles are
developed on the oral edge. The whole unit tends to be gently curved in a horizontal
plane, and is clearly transitional towards a pseudopolygnathid condition.

The basal bar is deepest anteriorly, and the anterior edge and antero-aboral
margin make an angle of about 70 ° with one another, so that the antero-aboral
angle protrudes strongly when seen in lateral view. The basal bar decreases in
depth posteriorly. The anterior third has a straight aboral margin, but the posterior
two thirds tend to be gently but continuously arched. The posterior end is bluntly
spatulate. The oral surface bears a series of closely spaced acicular denticles,
of which only the apices tend to be discrete. They are long, slender, and subequal

BRITISH AVONIAN CONODONT FAUNAS

241

in length. Single accessory lateral denticles are developed in the anterior half on
each side of the blade.

The basal cavity is situated slightly posterior to the mid-point of the unit. It is
very strongly flared laterally and shows a clear tendency to a pseudopolygnathid
development, but the cavity itself, in spite of its wide flaring lips, tends to be small.
It extends anteriorly and posteriorly as a shallow groove. The whole unit is gently
bowed inwards in a horizontal plane.

Genus TAPHROGNATHUS Branson & Mehl
1 94 1 Taphrognathns Branson & Mehl : 181 (non Welles 1947).
Type species. Taphrognathus varians Branson & Mehl.

Taphrognathus varians Branson & Mehl
Plate 13, figs. 4a-5d

1940 Taphrognathus varians Branson & Mehl : 182, PI. 6, figs. 27-33, 35-40.

1944 Taphrognathus varians Branson & Mehl ; Branson & Mehl : 246, PI. 94, figs. 66-68.

1947 Taphrognathus varians Branson & Mehl ; Cooper : 92, PI. 20, figs. 14-16.

1963 Taphrognathus varians Branson & Mehl ; Rexroad & Collinson : 21, PI. 1, figs. 18-20, 22.

1965 Taphrognathus varians Branson & Mehl ; Rexroad & Collinson : 24, PI. 1, figs. 30-32.

Material, ii specimens : figured, X 408, X 407.

Anterior blade

Posterior platform

Basal cavity

LATERAL VIEW

Carina

Median
trough

Posterior
carina

-Anterior blade

Basal cavity

Posterior platforr

ORAL VIEW ABORAL VIEW

Fig. 48. Taphrognathus sp. showing morphological terms used in the text.

242 BRITISH AVONIAN CONODONT FAUNAS

Range. Avon Gorge S 45-S 58.

Description. The distinctive feature of this species is its general elongate form
and its median anterior blade. This is continued posteriorly for a short distance on
the platform as a short carina. The median trough is narrow but deep, and the
whole platform is conspicuously lanceolate in oral view, with straight or only gently
convex lateral margins and a conspicuously pointed posterior end. The posterior
median part of the platform bears a nodose to sharp, short carina, which extends only
a short distance onto the platform beyond the posterior end, but is also extended
posteriorly beyond the termination of the platform proper. The blade tends to be
rather long, with fused denticles. The platform is smooth and V-shaped, and rela-
tively deep in relation to its width. It has regularly and bluntly crenulate lateral
margins and the whole platform tends to decrease in width aborally.so that theaboral
edge at the posterior end is more or less sharp. There is an elongated aboral cavity
below the anterior third of the platform which is shallow and flaring and more or less
symmetrical. It is extended anteriorly and posteriorly as a thin, slit-like excavation.

The anterior blade is deeper than the adjacent part of the posterior platform and
the denticles are bluntly tipped and coalesced.

The present specimens show some variation in the degree of posterior constriction,
in the development of the posterior carina, and in the form of denticulation of the
anterior bar.

Remarks. Rexroad & Collinson (1963 : 20) have shown that the genus Taphro-
gnathus and the genus Cavusgnathus are closely related and that in some faunas
transitional forms between these two genera can be seen. In our faunas transitional
forms are also found (PI. 13, figs. 1-3C). The medial blade of Taphrognathus appears
to move to take up an outer lateral position. However, since the blade is not
completely lateral, it is difficult to determine whether these specimens belong to the
genus Taphrognathus or to the genus Cavusgnathus. We have followed Rexroad &
Collinson in placing them as transitional species between the two genera. They can
be seen to be transitional, not only in the form of the anterior blade, but also in the
general outline of the cavity, and in the reduction of the posterior carina.

Gen. nov. A sp.
Plate 25, figs. 6a, b

Material, i specimen : figured, X 409.

Locality and horizon. North Crop. Sample ZLA 6.

Range. North Crop ZLA 6.

Description. The unit is of a hibbardellid type, but the anterior arch is
separated from the apical denticle by a short, denticulate, anterior bar. The anterior
arch is broken, but can be seen to be denticulate. The apical denticle is massive, sub-
circular in cross-section and is curved posteriorly. The posterior bar is thin and
finely denticulate.

In aboral view the unit is excavated, the basal cavity running from the apical

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5) &

a. j-» 4-)

DUN 82
DUN 81
DUN 80
DUN 79
DUN 78
DUN 77
DUN 76
DUN 75
DUN 74
DUN 73
DUN 72

I I

DUN 71
DUN 70
DUN 69
DUN 68
DUN 67
DUN 66
DUN 65
DUN 64
DUN 63
DUN 62
DUN 61
DUN 60
DUN 59
DUN 58
DUN 5 7
DUN 5 6
DUN 55
DUN 54
DUN 5 3
DUN 5 2
DUN 51
DUN 50

Fig. 57. Chart to show the ranges of conodont species in the Dunbar succession. Samples
DUN 50-71, Long Craig Upper Limestone : DUN 72-82. Skateraw Limestones : DUN
84, 85, Chapel Point Limestone : DUN 86, Dryburn Foot Limestone : DUN 87, 88,
Barnes East Limestone.

=Ui

— "_ 5 5 S

-*=> =

i = ■: --c

_l ! 1 1 1 \ 1 1 1 !_

BRITISH AVONIAN CONODONT FAUNAS 243

denticle anteriorly to the anterior arch beneath the anterior bar, and posteriorly to
where the posterior bar is broken.

Remarks. This form is unlike any other described conodont genus.

Gen. nov. B. sp.
Plate 25, figs, 7a, b

Material. 1 specimen : figured, X 410.

Range. Farlow ORZ 1.

Description. This specimen is one of problematical affinities ; its essential
features are that it has a conspicuous, elongated, main denticle, which is subtriangular
in cross-section, with a more or less sharp anterior edge. Its anterior aboral margin is
very flat, but has a narrow slit extending for a minute distance up the median part of
the face. It is recurved posteriorly, even though there is no posterior bar. Its base
is very thick-lipped and is regularly expanded as a relatively wide and deep cavity.
It appears that this anterior denticle is complete, though this is not certain. On the
outer lateral face, there is an anterior aboral process which makes an angle of about
90 ° with what would be the line of the posterior bar, and it is also depressed in a
vertical plane. Its anterior face is very convex in anterior view, and its anterior
distal end is straight-edged, with a sharp antero-aboral corner, but this is fractured in
the specimen. Its oral surface bears 3 denticles, of which the two innermost are
massive, with bluntly formed lateral edges and strongly convex anterior and posterior
faces. The denticle at the distal end is conspicuously smaller than the other two,
and the interior denticle, although very broad at the base, divides distally to give 2
separate denticles. There is a tendency for germ denticles to develop between the
larger denticles. The posterior lateral face of the anterior aboral process is flat and
the base is continuously excavated.

Remarks. The fact that this specimen appears essentially complete makes it
impossible to assign it to any existing genus. It may, in fact, represent a new one,
but it is possible that it is a broken specimen of Hindeodella corpulenta.

VII. SUMMARY AND CONCLUSIONS

(a) Scope of the present work

During the last decade, studies in both Germany and the United States have
demonstrated the potential value of conodonts in Carboniferous and Devonian strati-
graphical correlation. The present study represents a comprehensive description of
the conodont faunas of the British Lower Carboniferous, and a detailed analysis of
their stratigraphical distribution. This has been used to erect a zonal scheme, by
means of which a more precise correlation has been established between sections in
each of the main British Carboniferous depositional provinces than any yet available
on the basis of other faunal groups. Intercontinental correlations are also suggested.

244 BRITISH AVONIAN CONODONT FAUNAS

(b) Previoiis research

A critical review of previous research on Carboniferous conodont faunas is given,
together with a review of the present status of Carboniferous stratigraphical correla-
tion (p. 17).

Samples have been collected from each of five major depositional areas. This has
provided an indication of the degree of variability of conodont faunas both within
and between depositional basins. In all some 3! tons of limestone has been
processed.

Avon Gorge, Bristol

Detailed sampling of this area has involved the digestion of some 189 ' major '
rock samples, most of them about 10 lbs in weight. Every 10 ft. of the section
was sampled, and these samples were supplemented in critical parts of the succession
by others taken at 5 ft. and 2 ft. intervals. The stratigraphy of the collecting areas
is described in detail (p. 18).

North Crop of the South Wales Coalfield

A series of eleven localities in Brecknockshire and Monmouthshire was used to
construct a composite Lower Carboniferous section, and small collections were made
from Gower and Pembrokeshire. The middle part of the Avonian succession is
generally not fossiliferous in this area, but the higher parts of the Dibunophyllum
Zone have been used to complement the zonal scheme for the lower part of the
section, established in the Avon Gorge.

Shropshire

The thin development of the Z and K Zones at Farlow and Oreton have yielded
well-preserved faunas (p. 25).

Yorkshire

Sampling of the Yoredale succession in the type area has provided material for a
reconnaissance survey of Yoredale conodont faunas. They show close similarities to
those of the higher zones from the South Western Province.

Scotland

Extensive collections have been made from Dunbar, Roxburgh, Midlothian, Fife,
Ayrshire and Argyll. All the major limestones in the succession were sampled, some
at intervals of six inches, and most yielded well-preserved faunas.

(d) Methods of study

Most of the 25,000 specimens which form the basis of the study were extracted by
digestion of limestone in 8 % acetic acid. Methods of preparation and photography
are described. The abundance of conodonts in each sample has been recorded
(Figs 59-92)-

BRITISH AVONIAN CONODONT FAUNAS 245

(e) Stratigraphic ranges

The precise ranges of all conodont species recovered are shown by range charts
(Figs. 49-58). The ranges of the more stratigraphically useful genera and species
are described. Patrognathus gen. nov. is confined to the K Zone. Clydagnathus
gen. nov. is found in the K and Lower Z Zones of the North Crop and Shropshire, but
is rare in large faunas of the same age from the Avon Gorge. Siphonodella is very
rare in the Avonian, being confined to the Upper K Zone (p. 32).

Pseudopolygnathus extends from the basal K to the Ci Zone. It is represented by
numbers of short-lived species and is abundant in the Avon Gorge, but less common
in the North Crop (p. 32).

Gnathodus is a long-ranging Avonian genus, but individual species are valuable for
correlation in the Z, C and D Zones (p. 34). Spathognathodus is equally long-
ranging, but several short-lived species are valuable index fossils in various portions
of the succession.

Polygnathus ranges from the K to the top of the Ci Zone, and is represented by a
number of species. Mestognathus extends from the Ci to the D2 Zone (p. 35), while
Cavusgnathus is most characteristic of the C2, S and D Zones. Taphrognathus is
restricted to the Upper S2 Subzone (p. 35) in the south west, but occurs in the C
Zone of Roxburghshire.

Fourteen conodont assemblage zones are established

(f) Geographic variation

Our study shows several striking examples of what appear to be geographical
differences in contemporaneous conodont faunas. These include representatives of
the genera Siphonodella (p. 32), Pseudopolygnathus (p. 32), and Clydagnathus
(p. 32) among others. These differences reflect variation not only between faunas
separated by intercontinental distances, but also between faunas from the same
general depositional basin (e.g. the Avon Gorge and the North Crop). The degree of
such geographic variation is shown to be often greater than that generally admitted
by most conodont workers, and is an important consideration in stratigraphic
correlation. The absence of certain conodont genera and species from some areas
may represent either the absence of one or more groups of conodont-bearing animals
(conodontifers) of whatever taxonomic level, or the homoeomorphic replacement of
certain conodonts within the same broad type of natural assemblage of the cono-
dontifers.

(g) Correlation within the British Avonian

Avon Gorge-North Crop

The broad equivalence of Vaughan's coral-brachiopod zones as recognized in these
two areas is supported by a comparison of the conodont faunas. The basal K strata
of the North Crop are probably slightly younger than those of the Avon Gorge. The
Upper K Zone of the Avon Gorge is equivalent to the uppermost K and basal Z Zones
of the North Crop (p. 46).

2 4 6

BRITISH AVONIAN CONODONT FAUNAS

Abundance fnrtor = Total no.of specimens
Total weight o( sample

Total weight of sample
in kilograms

Fig. 59. Lithological section of the Cleistopora Zone in the Avon Gorge showing the
abundance factor of conodonts in each sample, and the total weight of each sample
dissolved in acetic acid. Samples K1-K17 were collected in the riverside section of the
Avon Gorge (ST 556746). Samples K 18-K 21 were collected in the quarry 1 of the Avon
Gorge (ST 557745), see Text-fig. 2.

BRITISH AVONIAN CONODONT FAUNAS

247

253
111

•FTT -

T7T

TTTT

3^E

"57^

j. : d ; j,

5^c:

5SJ 1

At A

i , ; i .' i

i , A t

3^-, i , ^

l -y l "V I -

JgE

& e>

""""■'

ft^v^M/ ■yv-,^

■I

Abundancefactor = Total no.of specimens
Total weight of sample

Total weight of
sample in kilograms

Fig. 60. Lithological section of the Lower and Upper Zaphrentis Zone in the Avon Gorge
showing the abundance factor of conodonts in each sample, and the total weight of each
sample dissolved in acetic acid. Samples Z i-Z 10 were collected in Quarry 1 (ST 557745),
Samples Z 11-Z 20 were collected in the Black Rock Quarry (ST 561747) and Samples
Z 21-Z 33 were collected in Quarry 2 (ST 561747).

248

BRITISH AVONIAN CONODONT FAUNAS

Abundance factors TotQl no of specimens Total weight of

Total weight ot sample sample in kilograms

Fig. 61. Continuation of the lithological section of the Upper Zaphrentis Zone (y Beds)
in the Avon Gorge showing the abundance factor of conodonts in each sample dissolved
in acetic acid. Samples Z 34-Z 38 were collected in Quarry 2 (ST 558745).

BRITISH AVONIAN CONODONT FAUNAS

249

zzz

±m±

i»i-i

MlTM'A

h 1 ■ 1

1~7~T

I \ I

est

1/1 /

-i-/-i-r

Abundance foctor = Totol no of specimens
Total weight of sample

Total weight of
sample in kilograms

Fig. 62. Lithological section of the Lower Caninia Zone in the Avon Gorge showing the
abundance factor of conodonts in each sample dissolved in acetic acid. Samples C i-C 1 1
were collected in the Railway Cutting (ST 559745) and Samples C 12-C 25 in Quarry 3
(ST 560744).

250

BRITISH AVONIAN CONODONT FAUNAS

C39- ?^-y

•/j/jf/jfrmTj}

warn

Bl I I I I I I I I I I I

Abundance factor = Total no of specimens
Total weight of sample

Totol weight of sample
in Kilograms

Fig. 63. Lithological section of the Upper Caninia Zone in the Avon Gorge showing the
abundance factor of conodonts in each sample dissolved in acetic acid. Samples were
collected from the roadside exposure (ST 562746).

BRITISH AVONIAN CONODONT FAUNAS

251

WrT'

E3E;

Trr

TTT-

Abundance mm nr- Total no of specimens
Total weight of sample

Total weight of
sample in Kilograms

Fig. 64. Lithological section of the Lower and Upper Seminula Zone in the Avon Gorge
showing the abundance factor of conodonts in each sample, and the total weight of
each sample dissolved in acetic acid. The samples were collected in the Great Quarry
(ST 56374°)-

2 5-

BRITISH AVONIAN CONODONT FAUNAS

i o IQIOICJ I

I 1 U 11 I

Abundonce factor: Totol no o( specimens
Total weight of sample

Total weight of
sample in kilograms

Fig. 65. Continuation of the lithological section of the upper part of the Seminula Zone
in the Avon Gorge showing the abundance factor of conodonts in each sample dissolved
in acetic acid. Samples S 22-S 30 were collected from the Great Quarry (ST 563740)
and Samples S 31-S 50 from the riverside exposure (ST 562737).

BRITISH AVONIAN CONODONT FAUNAS

^TT

III

i 't !' t| i

"VS I T .

Abundonce Toctor = Total no.of specimens
Total weight of sample

Total weight of
sample in kilograms

253

Fig. 66. Continuation of the lithological section of the uppermost part of the Seminula
Zone and Concretionary Bed in the Avon Gorge showing the abundance factor of cono-
donts in each sample dissolved in acetic acid. Samples S 51-S 72 were collected from
the riverside exposure (ST 562737).

254

BRITISH AVONIAN CONODONT FAUNAS

Abundance factor = Total no of specimens
Total weight of sample

Total weight of
sample in kilograms

Fig. 67. Lithological section of the Lower Dibunophyllum Zone in the Avon Gorge showing
the abundance factor of conodonts in each sample dissolved in acetic acid. Samples
D i-D 9 were collected from the roadside exposure (ST 564737).

BRITISH AVONIAN CONODONT FAUNAS

255

021 - :'-^ -r.

D20- '.tS-Jt

P17- I I I ~T

013 -~J

T-p..i>-f.o.'!?

Ill

11 1

P?^

ffi^

r^V-r

-i^Cn

1 . ' ; 1 . 1-

012 - ^ g

: i , t , r

TVT

III

Abundance factor= Total no, of specimens
Total weight of sample

5 10

TJTI

VMMA*

Total weight of
sample in kilograms

Fig. 68. Continuation of the lithological section of the Dibunophyllum Zone in the Avon
Gorge showing the abundance factor of conodonts in each sample dissolved in acetic acid.
Samples D to D 22 were collected from the roadside exposure (ST 564737).

256

BRITISH AVONIAN CONODONT FAUNAS

Abundance fnrtnr- Total no. of specimens
Total weight of sample

^iiiln

Total weight of

sample in

kilograms

Fig. 69. Lithological section of the upper beds of the Dibunophyllum Zone in the Avon
Gorge showing the abundance factor of conodonts in each sample dissolved in acetic
acid. Samples D 23-D 27 were collected from south of Bridge Valley Road (ST 564736).

BRITISH AVONIAN CONODONT FAUNAS

257

O 5 10 15 20

,„ Total no. of specimens Total weiqhtof sample

Abundance factor = . ki ? nnr .„ m .

Total we ght of sample ' n kilograms.

Fig. 70. Lithological section of the K Zone of the North Crop of the South Wales Coalfield
showing the abundance factor of conodonts in each sample, and the total weight of
limestone dissolved. For details of collecting localities see Fig. 7 and also p. 25.

25S

BRITISH AVONIAN CONODONT FAUNAS

Abundance factor , Total no. of specimens
Total weight of sample

Total weight of sample
in kilograms

Fig. 71. Lithological section of the Z and S2 Zones of the North Crop of the South Wales
Coalfield showing the abundance factor of conodonts in each sample, and the total weight
of limestone dissolved. For details of collecting localities see Fig. 7 and also p. 25.

BRITISH AVONIAN CONODONT FAUNAS

259

L o- 1 -

CYD

Abundance foctor = Total no. of specimens
Total weight of sample

-J

5 10 15
1 11 1 1 J I 1 1 I

I
1

Sfl i 1 1 1 1 1 il 11 1

10 15

Total weight of sample
in kilograms

Fig. 72. Lithological section of the D2 Subzone of the North Crop of the South Wales
Coalfield showing the abundance factor of conodonts in each sample, and the total weight
of limestone dissolved. For details of collecting localities see Fig. 7 and also p. 33.

26o

BRITISH AVONIAN CONODONT FAUNAS

5 10 15

Abundance factor: Total noof specimens
Total weight of sample

Total weight of somple
in kilograms.

Fig. 73. Lithological section of the D3 Subzone of the North Crop of the South Wales
Coalfield showing the abundance factor of conodonts in each sample, and the total
weight of limestone dissolved. For details of collecting localities see Fig. 7 and also p. 23.

BRITISH AVONIAN CONODONT FAUNAS

261

5 10 15 20

I — »0 7— ■

l_78 4

41 2

6 '2"

FAR 7

fc-=i/rV

FAR7A

6lt COVERED

IFAR6 g

6 ft COVERED

FAR 5

T^T ^(

T^, 5 ^

20 ft COVERED

Abandonee factor: Total no of specimens
Total weight of sample

TTTTTTTTTT

1 1 1 1 1 1 1 1 1 1 1 1 1

5 10 15 20

Total weight of sample
in kilograms

Fig. 74. Lithological section of the Cleistopora Zone at Farlow, Shropshire (Map reference
SO 642808), showing the abundance factor of conodonts in each sample and the weight
of each sample dissolved.

262

BRITISH AVONIAN CONODONT FAUNAS

TTT

urn

3L_L

Abundance ■

No of specimens
Total weight of sample

Total weight of
sample in
kilograms

Fig. 75. Lithological section of the Zaphrentis Zone in Oreton Quarry, Shropshire, (SO

648806).

Abundance factor: Total no. of specimens
Total weight of sample

Total weight of sample
in k i I o g ra m s

Fig. 76. Composite lithological section through the Yoredale Group (Hawes Limestone
to base of Simonstone Limestone) in the Gayle Beck — Hawes area (34/864883).

BRITISH AVONIAN CONODONT FAUNAS

263

Abundance factor =

Total no of specimens
Total weight of sample

Total weight of
sample in
kilograms.

Fig. 77. Composite lithological section through the Yoredale Group (base of Simonstone
Limestone to the top of the Five Yard Limestone inclusive) in the Snaizeholme — Hawes
area (34/815840). S. Ls. = Simonstone Limestone : F.Y. Ls. = Five Yard Limestone.

T~7

BEE

'.''.'"^"j - '.*

gUVLHLU

eovcprn

COVERED

>M I I I I I II I I I I I

I I II I I I I I I I I I I

Abundance fnrw- Totol no. of specimens
Total weight of sample

Total weight of sample
in kilograms.

Fig. 78. Composite lithological section through the Yoredale Group (top of the Five
Yard Limestone to the top of the Underset Limestone inclusive) in the Snaizeholme —
Hawes area (34/815840). T. Y. Ls.=Three Yard Limestone : U. Ls. = Underset
Limestone.

264

BRITISH AVONIAN CONODONT FAUNAS

-10

-0 - 1 -

5 10 15 20

1 1 1 hum 1 1 11 1 1 1 i i i

_i_

11 1 1 1 1 11 1 li 11 1 111 1 1

Abundance foctor=

40 60 80

Totol no of specimens
Total weight of sample

3 5 10 >5 20

Total weight of sample
in kilograms.

Fig. 79. Lithological section of part of the Lower Limestone Group in the Dunbar area :
the Long Craig Upper Limestone, showing the abundance factor for each sample and
the weight of each sample dissolved. For localities see p. 30.

BRITISH AVONIAN CONODONT FAUNAS

265

10 15 20

Abundance factor: Total no. of specimen. Totol we.ght of sample

Total weight of sample in kilograms.

Fig. 80. Lithological section of part of the Lower Limestone Group in the Dunbar area :
the Scateraw Lower Limestone to the Scateraw Upper Limestone, showing the abundance
factor of each sample and the total weight of each sample dissolved. For localities see
p. 30.

266

BRITISH AVONIAN CONODONT FAUNAS

eo'y

r.: T -.:T.

X.'-i.'. XI
-..!

r- ■ ■ t-

z>-

DUN 88

i i i

'iii

i ' i i

■ ' ' ■ '

cnuj-i

DUN 87

1 i ' i ' i

i i i

t r

■T---T--

"[ TV

wwwvwi

.T.-p.'. T

T X

T? T

T- ' • T
r - ...

T--..V

T T"

crOoo

QltJ

DUN 8G

I I

III

1 1 1

| 11

TT'T-

tL'"ti:

Til' T U

-20

D
D
X

o
/>

TH" T l'

ti:"t-i;

T^"T1'
T"— " *T ^'

ti.-t .:■

T-TS

TUJT^-

T T

T1L"T".1"

T^l'TV.!"

T^'T'M'1

T 1 1

=X4

i/i

»-
z

DUN 85

'■'■'■

l l 1

i i 1

I'll

1 1 1

III

ill

III

',',',

1 ' 1 ' 1 '

III

-1
LI
0.
<

1 1 1

III

DUN 84

'■ ■ ■ '■

-f

l l l

III

1 1 ' 1 '

l l l

!■!■!■

i * i ' i ii

iii 1
.,.1,1,1,1

1 T 1

, -X •

•-!-■'• T

... ., . j

■-T-'- ■ t y~

-0 ■■

:- x:^

.p. •/

5 10
MIIIIMI

20 40 60 80

Abundance factor ; Total no. of specimens
Total weight ol sample

Total weight of sample
in kilograms

Fig. 8i. Lithological section of part of the Lower Limestone Group in the Dunbar area :
the Chapel Point Limestone to the Barness East Limestone, showing the abundance
factor of each sample and the weight of each sample dissolved. For localities see p. 30.

BRITISH AVONIAN CONODONT FAUNAS

267

-60

-50

-40

-30

-20

-10

5 10 15

10 15

Abundance foctor= Totol no of specimens Total weight of sample
Total weight of sample in kilograms

Fig. 82. Lithological succession of part of the Lower Limestone Group in Midlothian :
the " Gilmerton " Limestone, showing the abundance factor of each sample and the
weight of each sample dissolved. This limestone may not be the true Gilmerton
Limestone (see p. 50). For localities see p. 30.

.'68

BRITISH AVONIAN CONODONT FAUNAS

5 10
M"imi|iiii

U i I i i 1 1

20 40 60 80 5 10 15

Ah..r,H/-.r,^4. « „ ^ i « . Total no of specimens

Abundance factors —

Total weight of sample

Total weight of sample
in kilograms

Fig. 83. Lithological section of part of the Lower Limestone Group in Midlothian :
the North Greens Limestone, showing the abundance factor for each sample and the
weight of each sample dissolved. For localities see p. 30.

BRITISH AVONIAN CONODONT FAUNAS

269

r35

■30

-20

5 10 15

I I I M 1 1 | 1 M I J

*t..„^_„,_ („,. Total no of specimens

Abundance factor =

Total weight ot sample

5 10 15

Total weight of
sample in
Kilog rams

Fig. 84. Lithological section of part of the Lower Limestone Group in Midlothian : the
Bilston Burn Limestone, showing the abundance factor and total weight of sample
dissolved for each sample. For localities see p. 30.

270

BRITISH AVONIAN CONODONT FAUNAS

L - 1 -

5 10 1!

JM I I I I 1 I I I I 1 I I

80 5 10 15

Abundonce foctor =

Totol no of specimen s
Total weight of sample

Total weight of sample
in k i I o g ra m s .

Fig. 85. Lithological succession of part of the Calciferous Sandstone Series of East Fife,
showing the fossiliferous limestones in the lower part of the succession. Coast section
from Hurlet Limestone near Coalfarm to Anstruther (NO 548027). Sample numbers
refer to detailed section given by J. W. Kirkby in Geikie (1902), p. 77 ff.

BRITISH AVONIAN CONODONT FAUNAS

271

-2 5

-20

SI 3

O *~

1 '

1 l(

V' v \ 1 "

v//.

10 15

100

5 10 15

abundance loctor = Totoi naofspecimens
Total weigh! 01 sample

Total weight of sample
in kilograms.

Fig. 86. Continuation of coast exposure of Fig. 85. Lithological section of part of the
Lower Limestone Group in East Fife : Hurlet and Hosie Limestones, showing abundance
factor for each sample and weight of each sample dissolved.

-7-

BRITISH AVONIAN CONODONT FAUNAS

1 1 ii 1 1 1 1 1 1 1

i i ' ■

Abundance factor

Total no of specimens
Total weight of sample

Total weight of

sample

in kilograms

Fig. 87. Lithological section of part of the Lower Limestone Group in North Ayrshire :
the Dockra Limestone, showing abundance factor for each sample and weight of each
sample dissolved. For localities see p. 30.

5 10
1 1 1 mil ii

Abandonee factor; Tot °' no. of specimens
Total wel qht of sample

Total weight of sample
in kilograms

Fig. 88. Lithological section of part of the Calciferous Sandstone Series in North Ayrshire,
showing the abundance factor of each sample and the total weight of each sample
dissolved. For localities see p. 30.

BRITISH AVONIAN CONODONT FAUNAS

273

11 111 1

Abundance factor =

Total no. of specimens Total weight of sample

Total weight of sample

in kilograms

Fig. 89. Lithological section of part of the Lower Limestone Group of North Ayrshire :
the Hosie Limestone, showing the abundance factor for each sample and the weight of
each sample dissolved. For localities see p. 30.

*74

BRITISH AVONIAN CONODONT FAUNAS

5 10 13 20

I I I I 1 1 I II | I I I I I I I I I

I I I I I I I | I I I I I I I I I

ak. „,■„„,„ <„- ( „, Total no. of specimens

Abundance factor = c

Total weight of sample

Total weight of sample
in kilograms

Fig. 90. Lithological section of part of the Upper Limestone Group of North Ayrshire :
the Index Limestone to the Upper Linn Limestone, showing the abundance factor for
each sample and the weight of each sample dissolved. For localities see p. 30.

BRITISH AVONIAN CONODONT FAUNAS

275

f- 40 "I—

5 10 15

Abundance factor = Total weight of sample

Total no. of specimens in kilograms

Total weight oi sample

Fig. 91. Lithological section of the Lower Algal Limestone " Series " of Harden Burn,
Roxburghshire, (NY 517907) showing the abundance factor for each sample and the
weight of each sample dissolved.

276 BRITISH AVONIAN CONODONT FAUNAS

Mid-Avonian unconformity in some places in the North Crop, and the absence of
conodonts in others, does not allow comparisons of the middle part of the succession,
although the uppermost Z of the Avon Gorge is younger than that of the North Crop.
The base of the D2 Subzone corresponds in both the Avon Gorge and the North
Crop. Few D2 or D3 conodonts have been recovered from the Avon Gorge (Figs.
67-69).

Shropshire

The lowest K strata at Farlow appear to be younger than those of the Avon Gorge,
or the North Crop. The Shropshire K Zone strata represent a very condensed
deposit. The higher part of the K Zone at Farlow is equivalent to the Lower Z of the
Avon Gorge. The Z Zone at Farlow represents the Spathognathodus costatus costatus-
Gnathodus delicatus Zone.

Yorkshire

The lowermost Yoredale limestones (the Gayle and the Hawes) have yielded few
conodonts. The overlying Hardraw Scar Limestone and Simonstone Limestone fall
within the Gnathodus mononodosus Assemblage Zone, and the Middle and Five Yard
Limestones within the Gnathodus girtyi collinsoni Assemblage Zone.

Scotland

A correlation is suggested between the Fife, Midlothian, Ayrshire, Dunbar and
Glengarnock successions, and between these and the South Western Province. The
Scottish sections all fall within the Gnathodus mononodosus or Gnathodus girtyi
collinsoni Zones, except for the lowest part of the Ayrshire succession and the Lower
Algal " Series " of Roxburghshire. Details of the correlations are given in Fig. 15.

(h) Intercontinental correlation

A critical review of North American and European Lower Carboniferous conodont
faunas is given (p. 52), and the correlation of these with the British Avonian is
summarized in Figs. 12, 16. The K Zone of the Avonian, represented by the two
lowest conodont zones and by the lower part of the Spathognathodus cf. S. robustus-
S. tridentatus Zone, is probably equivalent to the Lower Hannibal-Upper Chouteau
succession of the Mississippi Valley (Cu I-Cu II a). This would imply a very con-
siderable unconformity below the " Sedalia Formation " (Lower Cu II (3-y) which is
correlated with the Polygnathus lacinatus Zone of the Upper Z2 Beds. An alternative
correlation, based upon the first appearance of Gnathodus delicatus, would equate the
Spathognathodus costatus costatus-Gnathodus delicatus Zone of the Middle Z Zone
with the Upper Chouteau (Cu II a) (p. 56). The highest Z Zone is equivalent to
the Fern Glen and lower part of the Burlington Formations (Middle Cu II (3-y).

The Ci Subzone of the Avonian is of Upper Cu II [3-y-Lower Cu II 8 (Middle and
Upper Burlington) age, and the C2S1 and S2 Subzones of Upper Cu II 8 age.
(Keokuk to Lower St. Louis).

The D] Subzone is of Cu III a age, the D2 Subzone of Cu III a-Cu III (3 age, and
the D3 Subzone of Cu III (3-y age.

LEGEND FOR LITHOLOGICAL SECTIONS

CLASTIC SEDIMENTARY OTHER SEDIMENTARY ROCKS GENERAL
ROCKS AND STRUCTURES

o
o o

Gravel

Limestone

Lithified

formation

1 I

Conglomeratic
arkose

Fossil-fragment
limestone

Covered

Coarse-grained
sandstone

?i?

Detrital
limestone

'///>

Red beds

i • i

3?S

Conglomeratic
sandstone

91?

Limestone
breccia

2 5% sand
7 5°/. clay

|o|

Calcareous
sandstone

o 1 o

Oolitic
limestone

Lateral
transition

1 o |

■

Slightly sandy
formation

® 1 ©

Pi sol it i c

limestone

\7 ^7
<C7

Chert

l®l

-r~ ' • ' '

Siltstone

X | X

Crystalline
li mestone

Cherty
format i on

|x|

Clay

CD | CD

Sucrose

limestone

<2>

Concretions

1=1

Stratified
clay

y j

Dolomite

Algoe

/ /

Argillaceous
formation

J /

Dolomitic
h mestone

Corals

/ 1

Shale

rrr

Calcareous
formation

■

Brachiopods

Thin coal bed

^ ^

Marl

Fossils in
general

A A

Fine clay

— | —

Argillaceous
limestone

Bryozoa

l-l

Shale lenses

-T-r-
• nzn

Colcareous
lenses

Cnnoids

Silt

Dolomit ic

lenses

Carbonaceous
shale

Fig. 92. Composite legend for the lithological sections shown in the text.

BRITISH AVONIAN CONODONT FAUNAS 277

(i) Systematic palaeontology

The total fauna described includes some 25,000 identifiable specimens, referable to
167 species. These are described and illustrated, and their precise stratigraphical
ranges recorded. Two new named genera, 40 new species and 13 new subspecies
are recognized.

(j) Detailed lithological sections and abundance figures are included for each part of
the succession. Range charts are also provided.

VIII. ACKNOWLEDGMENTS

We are deeply indebted to our colleagues in the Geology Department, University
College of Swansea, for help and advice during the course of this study. Mr. T. R.
Owen has given us the benefit of his extensive knowledge of the Avonian rocks of
South Wales, and has been a particular help to us in planning our collecting in that
area. Mr. Brian Simpson has assisted us with various aspects of the technical work
involved in the study. We owe a particular debt of gratitude to Mrs. Shirley
Osborn and Mr. Michael Reynolds, for their patient help in rock processing, to Miss
Sonia Kostromin for her enormous secretarial help, to Mr. Stanley Osborn for his
skilful photography, to Mrs. Greir Lewis and Mrs Beryl Fisher who have prepared
the text-figures, to Miss Rhiannon Watkins for typing, and to Miss Veronica Arlen
and Mr. H. A. H. McKee for their editorial help.

We have been greatly helped by the generous advice of a large number of friends
in various countries, who have willingly discussed problems of systematics and
correlation with us, and have in some cases provided topotype material for com-
parison. We particularly wish to thank Dr. Gunther Bischoff of Gewerkshaft
Elwerath Erdolwerke, Hannover, Dr. Charles W. Collinson of the Illinois Geological
Survey, Dr. Raphael Conil of the Catholic University of Louvain, Professor Brian F.
Glenister of the University of Iowa, Professor F. Hodson of Southampton University,
Dr. John Huddle of the U.S.G.S., Washington, Dr. Huw Jenkins of Sydney Univer-
sity, Dr. Gilbert Klapper of Pan American Petroleum Corporation, Tulsa, Oklahoma,
Dr. M. Lys of the Institut Francais du Petrole, Dr. S. C. Matthews of the University
of Bristol, Dr. Klaus-Dieter Meischner, of the University of Gottingen, Dr. D. Moore
of Southampton University, Dr. Carl Rexroad of the Indiana Geological Survey,
Dr. James W. Scatterday of the State University of New York at Geneseo, Dr.
Trevor Walker of Long Beach College, California, Mr. R. B. Wilson of the I.G.S.,
Edinburgh, and Dr. Willi Ziegler of the Geologisches Landesamt Nordrhein-West-
falen.

We are also grateful for the financial support which made this study possible.
The Department of Scientific and Industrial Research, and its successor, the Science
Research Council, made a grant to F. H. T. Rhodes, to support a programme of
research, of which this study forms a major part. This grant provided support for
E. C. Druce, and R. L. Austin received a D.S.I.R. Studentship. We are also grateful
for the support in the form of accommodation, apparatus, materials and technical
help provided by the University College of Swansea.

278 BRITISH AVONIAN CONODONT FAUNAS

The completion of much of the present paper has also involved help from other
sources which we wish to acknowledge. During 1965-66 F. H. T. Rhodes held a
National Science Foundation Senior Visiting Scientist Fellowship at Ohio State
University. The award of this Fellowship, and the warm hospitality provided by
the Geology Department at Ohio State are acknowledged with deep gratitude, as
is the typing assistance of Miss Emily Laws.

R. L. Austin gratefully acknowledges the facilities and assistance provided at
the University of Southampton during the past two years, and especially the con-
tributions of Mrs. B. Gilkes and Mrs. A. Dunkley.

The publication of the present paper owes much to the generous encouragement
and help of Dr. H. W. Ball, Dr. W. T. Dean, Mr. E. F. Owen and Mr. H. G. Owen of
the Palaeontology Department of the British Museum (Natural History).

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2QO BRITISH AVONIAN CONODONT FAUNAS

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BRITISH AVONIAN CONODONT FAUNAS 291

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292 BRITISH AVONIAN CONODONT FAUNAS

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BRITISH AVONIAN CONODONT FAUNAS

293

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Manuscript submitted 6th March, 1967

X. APPENDIX

(a) Sample Register
The following prefixes are used for sample numbers

K Zone

North Crop Limestone

KSh

K Zone

North Crop Shale

Z Zone

North Crop Limestone (ten feet samples)

ZLA

Z Zone

North Crop Limestone (two feet samples)

ZSh

Z Zone

North Crop Shale

C 2 Si Zone

North Crop Limestone

CSh

C2S1 Zone

North Crop Shale

S2 Zone

North Crop Limestone

1 DL

Di Zone

North Crop Limestone

CYD

D 2 Zone

North Crop (Craig-y-Dinas)

2DL

D2 Zone

North Crop Limestone

2D Sh

D2 Zone

North Crop Shale

D3 Zone

North Crop Owen & Jones numbers

FAR

K Zone

Farlow

ORZ

Z Zone

Farlow (Oreton)

HAR

Ci Zone ?

Harden Burn, Roxburgh (Lower Algal limestone)

DUN

L. Limestone Group

Dunbar

GILM

Gilmerton Limestone

Midlothian

BIL 1-,

Beds below North Greens Limestone

BIL 100 +

Bilston Burn Limestone

Midlothian

NGL

North Greens Limestone

Midlothian

VEX

Lower Vexhim Limestone

Midlothian

ANS

Calciferous Sandstone Series

Fife

HOSIE

Hosie Limestones

Fife

HURLET

Hurlet Limestone

Fife

GO-IN

DR-IN

Index Limestone

Ayrshire

LIN-L

Lower Linn Spout Limestone

Ayrshire

204

BRITISH AVONIAN CONODONT FAUNAS

U-LIN

BRAU

ADOC

GLEN

MAC

SCC

GUD

K
Z
C
S
D
Y

Upper Linn Spout Limestone
Broadstone Limestone
Dockra Limestone
Hosie Limestones
Lower Limestone Series
C Zone

Ayrshire

Glengarnock, Ayrshire

Macrihanish, Argyll

Fall Bay, Gower, South Wales

Upper Devonian Germany, Honnetal
Upper costatus Zone to VI

K Zone Avon Gorge Limestone

Z Zone Avon Gorge Limestone

C Zone Avon Gorge Limestone

S Zone Avon Gorge Limestone

D Zone Avon Gorge Limestone

Yoredale Limestone Yorkshire

Map references for all localities are given in the text-figure explanations and on p. 18-31.

Slide

Nos of

figured

specimens

36 -

59 <

X 60

Name of Conodont

Angulodus walrathi (Hibbard)
sp. nov. B
sp. nov. C
sp. nov. C
sp. nov. D
sp. nov. D

Apatognathus varians Branson & Mehl
sp. nov. A
chauliodus Varker
bladus sp. nov.
bladus sp. nov.
scalenus Varker
scalenus Varker
scalenus Varker
petilus Varker
petilus Varker
petilus Varker
petilus Varker
geminus (Hinde)
geminus (Hinde)
geminus (Hinde)
geminus (Hinde)
cf . libratus Varker

Cavusgnathus charactus (Rexroad)

Apatognathus sp.

Sample Number

KL 19
ZLA 14
ZLA 10
ZLA 14
ZLA 11
ZLA 11
ZLA 13
ZLA 13
HOSIE 2 B
CYD 7A
CYD 7A
HOSIE 2 B
HOSIE 2 B
HOSIE 2 B
HOSIE 2 A
HOSIE 2 A
HOSIE 2 A
3D 14/15 XL 13
DUN 54
DUN 54
HOSIE 2 B
HOSIE 2 A
HOSIE 2 A
HAR 13
HOSIE 2 A

BRITISH AVONIAN CONODONT FAUNAS

295

Slide Nos of

figured

Name of Conodont

specimens

X61

Cavusgnathus charactus (Rexroad)

X62

charactus (Rexroad)

X63

convexus Rexroad

X64

cristatus Branson & Mehl

X65

naviculus (Hinde)

X66

naviculus (Hinde)

X67

naviculus (Hinde)

X68

naviculus (Hinde)

X 69

naviculus (Hinde)

X 70

? sp. nov. A

X71

Clydagnathus cavusformis gen. et. sp. nov.

X 72

cavusiformis gen. et. sp. nov.

X73

cavusiformis gen. et. sp. nov.

X74

cavusiformis gen. et. sp. nov.

X75

cavusiformis gen. et. sp. nov.

X 76

darensis gen. et. sp. nov.

X77

darensis gen. et. sp. nov.

X 78

gilwernensis gen. et. sp. nov.

X79

unicornis gen. et. sp. nov.

X80

unicornis gen. et. sp. nov.

X8I

unicornis gen. et. sp. nov.

X 82

gen. et. sp. nov. A

X83

Euprioniodina caverna (Collinson & Druce)

X84

microdentata (Ellison)

X85

sp.

X 86

sp. nov. A

X 87

Gnathodus delicatus Branson & Mehl

X 88

simplicatus sp. nov.

X 89

simplicatus sp. nov.

X90

simplicatus sp. nov.

X91

simplicatus sp. nov.

X92

Gnathodus ? sp. nov.

X93

bilineatus (Roundy)

X94

bilineatus (Roundy)

X95

commutatus. Branson & Mehl

X96

commutatus. Branson & Mehl

X97

commutatus. Branson & Mehl

X98

cuneiformis. Mehl & Thomas

X99

girtyi collinsoni subsp. nov.

X 100

girtyi collinsoni subsp. nov.

X 101

girtyi collinsoni subsp. nov.

X 102

girtyi collinsoni subsp. nov.

X103

girtyi girtyi Hass

X 104

girtyi girtyi Hass

XI05

girtyi girtyi Hass

X 106

girtyi girtyi Hass

X 107

girtyi simplex Dunn

X 108

girtyi simplex Dunn

X 109

Ozarkodina cf. elegans (Stauffer)

Sample Number

HAR 13
HAR 13

3D i4/!5
3D 22

HOSIE 2 B
Gilm 2

3D I4A5
3D 14/15
HOSIE 2 A
ZLA 32
KL7
KL2
KL5
KL 5
KL5
ZLA 13
ZLA 27
KL 1
ZLA 14
ZLA 14
ZLA 11
KL I3

3D 14/15
GILM 2
K 14

HOSIE 2 B
ZLA 6
Z38
ZLA 33
ZLA 33
ZLA 33
ZL8
3 d 14/15
3D 14/15
3D 14/15
3D 14/15
3D 12
S 11

3D 14/15
3D 14/15
3D 14/15
3D 14/15
HOSIE 2 A
HOSIE 2 A
HOSIE 2 A
HOSIE 2 A
HOSIE 2 A (1)
HOSIE 2 A 5
Z 19

296

BRITISH AVONIAN CONODONT FAUNAS

Slide Nos of
figured
specimens
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X

13
14
15
16

17
18

23
24
25
26

27
28

29
30
31
32

33
34
35
36
37
38
39
40

4i
42
43
44
45
46

47
48

50
5i
52
53
54
55
56
57
58
59

Name of Conodont

Gnathodus girtyi simplex Dunn
girtyi simplex Dunn
girtyi soniae subsp. nov.
girtyi soniae subsp. nov.
girtyi soniae subsp. nov.
girtyi soniae subsp. nov.
girtyi turritus Collinson & Druce
girtyi subsp. nov.
girtyi subsp. nov.
girtyi subsp. nov.
homopunctatus Ziegler
homopunctatus Ziegler
homopunctatus Ziegler
homopunctatus Ziegler
mononodosus sp. nov.
mononodosus sp. nov.
mononodosus sp. nov.
nodosus Bischoff
nodosus Bischoff
nodosus Bischoff
Polygnathus sp.
Gnathodus punctatus (Cooper)
punctatus (Cooper)
punctatus (Cooper)
symmutatus sp. nov.
symmutatus sp. nov.
symmutatus sp. nov.
symmutatus sp. nov.
sp.
Hibbardella (Hibbardella

(Hibbardella

Sample Number

A
A

) acuta Murray & Chronic

) milleri Rexroad

) ortha Rexroad

) parva sp. nov.

) cf. macrodentata Thomas

) cf . macrodentata Thomas

) cf. macrodentata Thomas

(Hassognathus) separata (Branson & Mehl)

(Roundya) barnettana Hass

(Roundya) barnettana Hass
Pseudopolygnathus vogesi sp. nov.
Hindeodella antecomplex Collinson & Druce

antecomplex Collinson & Druce

cooperi (Elias)

HOSIE 2
HOSIE 2
3D 8
3D 12
3D 14/15
3D 14/15
3D 23
CYD 7 A
CYD 7 A
CYD 7 A
3D 14/15
3D 14/15
3D 14/15
3D 14/15
3D 14/15
3D 14/15
3D 14/15
3D 14/15
3D 14/15
HOSIE 2
(SL 461) D 22
Z38
Z38
Z38
3D 10
3D 10
3D 14/15
3D 14/15
HOSIE 2 A
3D 14/15
HOSIE 2
HOSIE 2
HOSIE 2
HOSIE 2
3D 14/15
3D 14/15
ZLA 32
ZLA 32
KL3
ZLA 6
ZLA 7
3D 14/15
3D 14/15
HOSIE 3D 23
HOSIE 2 C
K 12
3D 14/15
3D 17
3D 14/15
3D 14/15

A
B

BRITISH AVONIAN CONODONT FAUNAS

297

Slide Nos of

figured

Name of Conodont

specimens

X 160

corpulenta Branson & Mehl

X 161

corpulenta Branson & Mehl

X 162

croka Collinson & Druce

X163

croka Collinson & Druce

X 164

croka Collinson & Druce

X165

croka Collinson & Druce

X 166

Spathognathodus costatus costatus (E. R. Bra

X 167

hibbardi Collinson & Druce

X 168

hibbardi Collinson & Druce

X 169

hibbardi Collinson & Druce

X 170

ibergensis Bischoff

X 171

ibergensis Bischoff

X 172

ibergensis Bischoff

XI73

ibergensis Bischoff

XI74

ibergensis Bischoff

XI75

montanaensis (Scott)

X 176

montanaensis (Scott)

XI77

subtilis Ulrich & Bassler

X 178

subtilis Ulrich & Bassler

XI79

subtilis Ulrich & Bassler

X 180

subtilis Ulrich & Bassler

X 181

secarata Collinson & Druce

X 182

secarata Collinson & Druce

XI83

secarata Collinson & Druce

X 184

secarata Collinson & Druce

X 185

undata Branson & Mehl

X 186

sp. nov.

X 187

tenuis Clarke

X 188

Hindeodus sp.

X 189

sp.

X 190

sp.

X 191

sp.

X 192

alatoides (Rexroad & Burton)

XI93

alatoides (Rexroad & Burton)

X 194

imperfectus (Rexroad)

XI95

Kladognathus clarensis Collinson & Druce

X 196

clarensis Collinson & Druce

XI97

macrodentatus (Higgins)

X 198

macrodentatus (Higgins)

X 199

macrodentatus (Higgins)

X 200

macrodentatus (Higgins)

X 201

Ligonodina beata nom. nov.

X 202

beata nom. nov.

X203

beata nom. nov.

X 204

levis Branson & Mehl

X205

levis Branson & Mehl

X 206

levis Branson & Mehl

X 207

levis Branson & Mehl

X 208

magnilaterina sp. nov.

X 209

magnilaterina sp. nov.

Sample Number

KL3
KL 19
3D 14/15
3D 14/15
GILM5
3D 14/15
ZLA6
3D 14/15 3
3D 14/15 5
3D 14/15 6
3D 14/15
3D 14/15
3D 14/15
HOSIE 2 A
GILM2
3 D 12
3D 12
ZLA33
ZLA33
ZLA33
ZLA 14
ZLA 3D 14/15
ZLA 3D 14/15
ZLA 3D 14/15
CYD7 A
3D 14/15
3D 14/15
GILM5
HOSIE 2 A
HOSIE 2 A
HOSIE 2 A
HOSIE 2 A
HOSIE 2 B
HOSIE 2 C
HOSIE 2 B
3D 10
3D 10
3D 14/15
3D 14/15
3D 14/15
DUN 54
KL19
ZLA 12
ZLA 12
HOSIE 2 A
HOSIE 2 A
HOSIE 2 B
HOSIE 2 B
HOSIE 2 C
HOSIE 2 C

BRITISH AVONIAN CONODONT FAUNAS

Slide Nos of
figured
specimens
X210
X 211
X212
X 213
X 214
X215
X 217
X218
X 219
X 220

X 221
X 222

X 223

X224
X225

X 226
X 227
X 228
X 229

X23I

X 232

X233

X234
X235

X236

X237
X238

X 239
X 240
X 241

X242

X243

X244

X245

X246

X247

X248

X 249

X250
X25I
X252

X253
X254
X255

X256

X257

X258
X259

X 260

X26I

Name of Conodont

magnilaterina sp. nov.
magnilaterina sp. nov.
osborni sp. nov.
osborni sp. nov.
roundyi Hass
roundyi Hass
sp. A
? sp.
? sp.
Apatognathus porcatus (Hinde)
Spathognathodus cyrius (Cooper)
Lonchodina bolbosa Collinson & Druce
bolbosa Collinson & Druce
bolbosa Collinson & Druce
furnishi Rexroad
furnishi Rexroad
furnishi Rexroad
furnishi Rexroad
obtunda Collinson & Druce
paraclarki Hass
paraclaviger Rexroad
paraclaviger Rexroad
transitans Collinson & Druce
transitans Collinson & Druce
transitans Collinson & Druce
Magnilaterella complectens (Clarke)
complectens (Clarke)
complectens (Clarke)
complectens (Clarke)
clarkei sp. nov.
spp.
sp.
sp.
Mestognathus beckmanni Bischoff
bipluti Higgins
bipluti Higgins
bipluti Higgins
bipluti Higgins
neddensis sp. nov.
neddensis sp. nov.
neddensis sp. nov.
Metalonchodina bidentata (Gunnell)
bidentata (Gunnell)
bidentata (Gunnell)
bidentata (Gunnell)
Neoprioniodus antespathatus Collinson & Druce
antespathatus Collinson & Druce
barbatus (Branson & Mehl)
barbatus (Branson & Mehl)
barbatus (Branson & Mehl)

Sample Numbei

HOSIE 2 C
HOSIE 2 C
3D 14/15
3D 14/15
DUN 54
3D 14/15
ZLA 32
ZLA 11
3D 10
DUN 58
KL 16
3D 14/15
3D 14/15
3D 14/15
HOSIE 2 C
HOSIE 2 C
DUN 54
GILM3
3D 14/15
3D 14/15
3D 14/15
3D 14/15
3D 14/15
3D 14/15
3D 10
HOSIE 2 B
HOSIE 2 B
HOSIE 2 B
HOSIE 2 A
BIL 102
HOSIE 2 A
DUN 76
GILM 2
SCC 29
ANS 15
ANS 15
CYD 7 A
CYD 6 A
CYD 6 A
CYD 6 A
CYD 7 A
3D 14/15
3D 14/15
3D 14/15
BIL 102
3D 14/15
3D 14/15
ZLA 11
ZLA 11
ZLA 13

BRITISH AVONIAN CONODONT FAUNAS

299

Slide Nos of
figured
specimens
X 262
X 263
X264
X 265
X 266
X 267
X 268
X 269
X 270

X27I

X 272

X273

X2 74

X275

X 276

X277

X 278
X 279
X 280

X28I

X 282
X 283

X284

X 285
X 286
X 287
X 288

X289

X 290

X29I

X 292
X 293
X 294

X295

X 296
X 297

X298

X 299
X 300

X30I

X 302

X303

X 304

X305

X 306

X307
X308

X 309
X 310

X3II

Name of Conodont

barbatus (Branson & Mehl)
confluens (Branson & Mehl)
confluens (Branson & Mehl)
conjunctus (Gunnell)
conjunctus (Gunnell)
conjunctus (Gunnell)
montanaensis (Scott)
montanaensis (Scott)
montanaensis (Scott)
montanaensis (Scott)
peracutus (Hinde)
peracutus (Hinde)
peracutus (Hinde)
peracutus (Hinde)
scitulus (Branson & Mehl)
scitulus (Branson & Mehl)
scitulus (Branson & Mehl)
spathatus Higgins
tulensis (Pander)
varians (Branson & Mehl)

sp. nov. A
cf. armatus (Hinde)
cf. camurus Rexroad
cf. camurus Rexroad
cf. camurus Rexroad
cf. camurus Rextoad
Ozarkodina cf. congesta Stauffer
curvata Rexroad
delicatula (Stauffer & Plummer)
delicatula (Stauffer & Plummer)
delicatula (Stauffer & Plummer)
hindei Clarke
hindei Clarke
hindei Clarke
macra Branson & Mehl
macra Branson & Mehl
macra Branson & Mehl
parva (Huddle)
plana (Huddle)
plana (Huddle)
plumula Collinson & Druce
plumula Collinson & Druce
macer (Branson & Mehl)
macer (Branson & Mehl)
sp.
sp.
sp.
Patrognathus variabilis gen. et. sp. nov.
variabilis gen. et. sp. nov.
variabilis gen. et. sp. nov.

Sample Number

ZLA 14

ZLA 33

HOSIE 2 B

HOSIE 2 C

3D 14/15

HOSIE 2 A

HOSIE 2 B VI 36

3D 14/15

DUN 54

3D 14/15

3D 17

ZLA 14

VEX 1

GILM 1

HOSIE 2 C

Z37
GILM 3

3D 4

3D 14/15

ZLA 31

HOSIE 2 B

HOSIE 2 A

GILM 5

K 4

K22

Z 18

K3
Kl 3

3D 12
3D 12

Z35

Z 3 8

K 13
Z 16
KL2
KL2
KL2

3°o

BRITISH AVONIAN CONODONT FAUNAS

Slide Nos of

figured

specimens

X312

x 313

X3M
X3I5
X316

X317
X 318

X3I9

X 320

X32I

X 322

X323
X324
X325

X 326

X392
X327

X328

X330
X33I

x 332

X333
X334
X335
X336
X337
X338

X339
X340

X34I
X342
X343

X344

X345
X346

X347
X348

X349

X350
X35I
X352
X353
X354
X355
X356
X357
X358
X359

X360
X36I

Name of Conodont

Plectospathodus ? sp. nov. A
sp. nov. A
sp. nov. B
Prioniodina eireica (Collinson & Druce)

laevipostica (Rexroad & Collinson)
laevipostica (Rexroad & Collinson)
Apatognathus sp.
Hibbardella (Hassognathus) sp.
Ligonodina tenuis Branson & Mehl
tenuis Branson & Mehl
Magnilaterella spp.
spp.
Hindeodella undata Branson & Mehl
Ozarkodina hindei Clarke
Apatognathus porcatus (Hinde)
Cavusgnathus unicornis Youngquist & Miller
Geniculatus sp.
Ligonodina tulensis (Pander)
Prioniodina oweni sp. nov.

prelaevipostica sp. nov.
prelaevipostica sp. nov.
prelaevipostica sp. nov.
prelaevipostica sp. nov.
prelaevipostica sp. nov.
prelaevipostica sp. nov.
slipans (Rexroad)
stipans (Rexroad)
stipans (Rexroad)
stipans (Rexroad)
subaequalis (Higgins)
subaequalis (Higgins)
subaequalis (Higgins)
subaequalis (Higgins)
? sp. nov.
Polygnathus communis communis Branson & Mehl
communis communis Branson & Mehl
communis communis Branson & Mehl
bischoffi sp. nov.
bischoffi sp. nov.
bischoffi sp. nov.
bischoffi sp. nov.

inornatus inornatus Branson & Mehl
inornatus inornatus Branson & Mehl
inornatus inornatus Branson & Mehl
inornatus rostratus subsp. nov.
inornatus rostratus subsp. nov.
inornatus vexatus subsp. nov.
inornatus vexatus subsp. nov.
lacinatus asymmetricus subsp. nov.
lacinatus asymmetricus subsp. nov.

Sample Number

ZLA33

3D 17

CYD 7 A

HOSIE 2A

DUN 77

3D 22

3D 14/15

3D 14/15 (not figured)

3D 12 (not figured)

HOSIE 2C (not figured)

S 49

DUN 59

CYD 3

ZLA 5

ZLA 11

ZLA 6

ZLA 33
ZLA 33

ZLA 33
3D 14/15
3D 14/15
3D 14/15
3D 14/15
3D 14/15
3D 14/15
3D 14/15
3D 14/15
GILM3
ZLA 14
ZLA 14
ZLA 14

sec
sec
sec

C 20
KLM 1
KLM 1
KL 19
KL 19
KL 19
KL 19
KLM 1
ZLA 33
ZLA 32

BRITISH AVONIAN CONODONT FAUNAS

301

Slide Nos of

figured Name of Conodont
specimens

X 362 lacinatus asymmetricus subsp. nov.

X 363 lacinatus asymmetricus subsp. nov.

X 364 lacinatus circaperipherus subsp. nov.

X 365 lacinatus circaperipherus subsp. nov.

X 366 lacinatus circaperipherus subsp. nov.

X 367 lacinatus circaperipherus subsp. nov.

X 368 lacinatus lacinatus Huddle

X 369 lacinatus lacinatus Huddle

X 370 lacinatus lacinatus Huddle

X 371 lacinatus prelobatus subsp. nov.

X 372 lacinatus prelobatus subsp. nov.

X 373 lacinatus prelobatus subsp. nov.

X 374 lacinatus prelobatus subsp. nov.

X 372 lacinatus prelobatus subsp. nov.

X 375 lobatus inflexus subsp. nov.

X 376 lobatus lobatus Branson & Mehl

X 377 lobatus lobatus Branson & Mehl

X 378 lobatus lobatus Branson & Mehl
X 379 Spathognathodus plumulus plumulus sp. et. subsp. nov.

X 380 plumulus plumulus sp. et. subsp. nov.

X 381 plumulus plumulus sp. et. subsp nov.

X 382 plumulus nodosus subsp. nov.

X 383 plumulus nodosus subsp. nov.

X 384 plumulus shirleyae subsp. nov.

X 385 plumulus shirleyae subsp. nov.

X 386 pulcher (Branson & Mehl)

X 387 cf. robustus (Branson & Mehl)

X 388 cf. robustus (Branson & Mehl)

X 389 scitulus (Hinde)

X 390 scitulus (Hinde) subsp. nov. A

X 391 scitulus (Hinde)

X 392 scitulus (Hinde)

X 393 scitulus (Hinde)

X 394 tridentatus (E. R. Branson)

X 395 tridentatus (E. R. Branson)

X 396 tridentatus (E. R. Branson)

X 397 tridentatus (E. R. Branson)

X 398 bischoffi sp. nov.

X 399 bischoffi sp. nov.

X 400 bischoffi sp. nov.

X 401 bischoffi sp. nov.

X 402 ziegleri sp. nov.

X 403 ziegleri sp. nov.

X 404 ziegleri sp. nov.

X 405 sp. A

X 406 sp. B
X 407 Taphrognathus varians Branson & Mehl

X 408 varians Branson & Mehl
X 409 Gen nov. A. sp.
X 410 Gen. nov. B. sp.

Sample Number

ZLA32
ZLA31
ZLA32
ZLA32
ZLA 32
ZLA 32
ZLA 31
ZLA 31
ZLA 31
ZLA 32
ZLA 32
ZLA 32
ZLA 32
ZLA 32
KLM 1
KLM 1
KL 19
KL 19
KL7
KL2 11
KL2 11
KL 1
KLi
KL2
KL3
ZLA 31
ZLA 10
ZLA 10
DUN 78
DUN 78
GILM 1
HOSIE 2 A
CYD 7 A
ZLA 14
ZLA 14
ZL8
KL 19
GUD 3
GUD 8
GUD 4
GUD 5
GUD 2
GUD 9
GUD 10
KL3 V
ZLA 5
HAR20
HAR 16
ZLA 6
ORZ 1

30-!

liklllSH AVON1AN CONODONT FAUNAS

Slide Nos i>

figured

specimens

X 41 1

X 412

X 413

X 4I4

x 415

X 416

X 417

X4I8

X4I9

X 420

X42I

X 422

X 423

X 424

X 425

X 426

X427

X 428

X429

X 430

X43I
X432

X433

X 434
X 435

X436

X437
X438

X439
X 440

X 441

X442

X 443
x 444
X445
X 446

X447
X 448
X 449
X 45°
X451
X452
X453
X 454
X455
X456

X457
X458

X 459
X 460

Name of Conodont

Sample Number

Gnathodus avonensis sp. now

antetexanus Rexroad & Scott
antetexanus Rexroad & Scott
antetexanus Rexroad & Scott
simplicatns sp. no v.
bilineatus (Roundy)
bilineatus (Roundy)
commutatus (Branson & Mehl)
Ozarkodina plana (Huddle)

compressa Rexroad
Gnathodus semiglaber Bischoff
Hibbardella acuta Murray & Chronic
sp.
Lonchodina sp. A
Gnathodus sp.

delicatus Branson & Mehl
Plectospathodus ? sp. nov. B
sp. nov. B
Prioniodina latericrescens (Branson & Mehl)
Polygnathus P. communis communis Branson & Mehl
Magnilaterella clarkei sp. nov.
clarkei sp. nov.
Pseudopolygnathus longiposticus Branson & Mehl
longiposticus Branson & Mehl
Spathognathodus cf. campbelli Rexroad

coaptus (Branson & Mehl)
ziegleri sp. nov.
Pseudopolygnathus dentilineatus E. R. Branson
Gnathodus bilineatus bilineatus (Roundy)
Polygnathus lobatus lobatus Branson & Mehl
Hibbardella {Hibbardella) sp.

Pseudopolygnathus cf. longiposticus Branson & Mehl

cf. longiposticus Branson & Mehl

longiposticus Branson & Mehl

Hindeodella sp.

Magnilaterella ? sp.

Pseudopolygnathus cf. longiposticus Branson & Mehl
cf. longiposticus Branson & Mehl
Spathognathodus cf. campbelli Rexroad
cf. campbelli Rexroad
cf. campbelli Rexroad
coaptus (Branson & Mehl)
coaptus (Branson & Mehl)
costatus costatus (E. R. Branson)
costatus costatus (E. R. Branson)
costatus sulciferus (Branson & Mehl)
costatus sulciferus (Branson & Mehl)
costatus sulciferus (Branson & Mehl)
crassidentatus (Branson & Mehl)

Z38

ZLA32

ZLA33

C 4

ZLA 32
3D 14/15
3D 14/15
3D 14/15

K 3

3D 22A
Z30

3D 14/15
ZLA 32
ZLA 32
HOSIE 2
Z 32

3D 14/15
3D 14/15
Z 22
KLM 1
BIL 102
DUN 54
Z38
Z38

3D 14/15
Z 36
GUD 7
Z17

3D 14/15
KL 19
KL 16
Z 38
Z38
Z38
Z38
ZLA 33
ZLA 37
Z 38
Z38

3D 14/15
3D 14/15
3D 14/15
Z38
Z 36
ZLA 6
ZLA 8
ZLA 6
ZLA 12
ZLA 12
ZLA 15

BRITISH AVONIAN CONODONT FAUNAS

303

Slide Nos of
figured
specimens
X461
X 462
X463
X 464

X465
X 466

X467

X 468

X469
X470

X47I
X472

X473

X474

X475
X476

X477
X478

X479

X 480

X48I
X482

X483

X484

X485

X486

X487

X 488
X 489
X 490
X 491
X 492

X493

X 494
X495
X 496
X497
X498
X 499
X 500
X 501

X502
X503

X504

X505

X 506

X507
X508

X 509

X5IO

Name of Conodont

crassidentatus (Branson & Mehl)
crassidentatus (Branson & Mehl)
crassidentatus (Branson & Mehl)
cristulus Youngquist & Miller
cristulus Youngquist & Miller
cristulus Youngquist & Miller
cristulus Youngquist & Miller
cristulus Youngquist & Miller
cf. cyrius (Cooper)
cf. cyrius (Cooper)
cf. cyrius (Cooper)
elongatus (Branson & Mehl)
elongatus (Branson & Mehl)
elongatus (Branson & Mehl)
elongatus (Branson & Mehl)
plumulus plumulus sp. no v.
Pseudopolygnathus dentilineatus E. R. Branson
dentilineatus E. R. Branson
dentilineatus E. R. Branson
dentilineatus E. R. Branson
dentilineatus E. R. Branson
expansus sp. nov.
expansus sp. nov.
multistriatus Mehl & Thomas
multistrialus Mehl & Thomas
multistriatus Mehl & Thomas
multistriatus Mehl & Thomas
nodomarginatus (E. R. Branson)
nodomarginatus (E. R. Branson)
nodomarginatus (E. R. Branson)
nodomarginatus (E. R. Branson)
nodomarginatus (E. R. Branson)
nodomarginatus (E. R. Branson)
nodomarginatus (E. R. Branson)
nodomarginatus (E. R. Branson)
postinodosus sp. nov.
primus Branson & Mehl
primus Branson & Mehl
primus Branson & Mehl
primus Branson & Mehl
vogesi sp. nov.

triangulus cf. pinnatus Voges
vogesi sp. nov.
vogesi sp. nov.
vogesi sp. nov.
vogesi sp. nov.
vogesi sp. nov.
Hibbardella abnormis Branson & Mehl
Gnathodus nodosus Bischoff
nodosus Bischoff

Sample Number

ZLA 15
ZLA 15
ZLA 15
HOSIE 2 A
HOSIE 2 A
HOSIE 2 B
VEX 1
GILM 1
KL 19
KL 16
KLM 1
KL20
ZLA 6
ZLA 10
ZL 8
KL 4
Z17
Z 16
Z 16
Z 16
Z 16
K 12
K 12
ZLA 33
Z 26
Z 26
Z 26
ZLA 31
ZLA 31
ZLA 31
ZLA 31
ZLA 32
ZLA 32
ZLA 32
ZLA 32
Z38
Z17
Z17
Z 22
Z17
KL2

c 7

K 12
K 12
KL 12
KL2

KL9
CYD 6
3D 14/15
3^ 14/15

3°4

Slide Nos of
figured
specimens
X 511
X512
X513
X5H
X515
X516

X517
X 518

X519
X520
X 521

X522

X523
X524
X525

X526

X527

X528
X529
X530
X53I
X532
X533
X534
X535
X536
X537
X538
X539

X540

X54I

X542

X543

X544

X545
X546

X547
X548

X 549
X550
X551
X552
X553
X554
X555
X556
X557
X558
X559
X 560

BRITISH AYONIAN CONODONT FAUNAS

Name of Conodont

Magnilaterella sp.

Spathognathodns pulcher (Branson & Mehl)
pulcher (Branson & Mehl)
Hindeodella brevis Branson & Mehl
Pseudopolygnathus sp. A
Polygnathus cf. communis Branson & Mehl
Magnilaterella contraria sp. nov.
Spathognathodns sp. nov.
Patrognathus variabilis gen. et. sp. nov.
Neoprioniodus cf. N. confluens (Branson & Mehl)
Gnathodns punctatus-Gnathodus semiglaber transition
Pseudopolygnathus cf. longiposticus Branson & Mehl
cf. longiposticus Branson & Mehl
Kladognathus mehli (Rexroad)

Gnathodus punctatus-Gnathodus semiglaber transition
Gen. et. sp. indet.
Lonchodina furnishi Rexroad
Magnilaterella robusta Rexroad & Collinson
robusta Rexroad & Collinson
Polygnathus inornatus rostratus sub. sp. nov.

sp.
Scaphignathus ? sp. A
sp. B
Siphonodella isosticha (Cooper)
isosticha (Cooper)
obsoleta Hass
sp. A
sp.
sp.
Spathognathodns anteposicornis Scott
anteposicornis Scott
anteposicornis Scott
anteposicornis Scott
Gnathodus antetexanus Rexroad & Scott
Pseudopolygnathus cf. longiposticus Branson & Mehl
primus Branson & Mehl
longiposticus Branson & Mehl
Magnilaterella robusta Rexroad & Collinson
Pseudopolygnathus primus Branson & Mehl
Apatognathus chauliodus Varker
Polygnathus inornatus vexatus sub. sp. nov.
Pseudopolygnathus cf . fusiformis Branson & Mehl
Magnilaterella contraria sp. nov.
Spathognatliodus cf. crislulus Youngquist & Miller
cf. cristulus Youngquist & Miller
cf. cristulus Youngquist & Miller
cf. cristulus Youngquist & Miller
Taphrognathus — Cavusgnathus transition
Taphrognathus — Cavusgnathus transition
Taphrognathus — Cavusgnathus transition

Sample Number

3D 12
Z35
Z35

3D 14/15
ZLA 31
KLM 140
HOSIE 2 B
Z 20
KL 2
KL 19
Z38
Z 38
Z38

3D 14/15
Z 38
ZLA 31
3D 23
DUN 78
DUN 78
KL 4
FAR 4 A
ZL2
ZLq
KL 16
KL 16
KLM 1
KL 16
K 12
K 17
ZLA 15
ZLA 15
ZLA 14
KL IQ

C 7
Z38
Z17
Z 38
DUN 78
Z 18

HOSIE 2B
KLM 1
C 14
ZLA 33
ZLA 33
ZL 18
ZLA 33
ZLA 33
S49
S 4 9
S49

INDEX

305

Abergavenny, 18

Acetic acid, 4

Africa, North, 64, 65

Alberta, 9

Algae, 4, 11, 20

Algal Series, 30, 51, 275, 277

America, North, 4, 5, 9, 43-45, 52-57, 59,

60-65, 77. 97- 106-107, 1 5°. 2 °8. 217. 277
Anchoralis Subzone, 57, 59, 64-65
Anchoralis-bilineatus interval, 64
Angulodus, 66

demissus, 68

gravis, 69

sp. nov. B, 66

sp. nov. C, 68, 69

sp. nov. D, 68, 69

walrathi, 66
Anstruther, 30, 270
Anthraconaia modiolaris Zone, 7
Apatognathus, 6, 35, 42, 48, 62, 69-77, 9°

bladus, 35, 44, 69, 70, 71

chauliodus, 71

geminus, 35, 42, 44, 71, 72

geminus — Cavusgnathus Assemblage Zone,
10, 44, 61, 62

petilus, 42, 72, 73

porcatus, 73, 74

scalenus, 35, 42, 74

cf. libratus, 43, 75, 76

sp-. 77

sp. nov. A, 76, 77

varians, 40, 69, 75
Arenigian, 5
Arnsbergian, 18
Argyll, 30, 244
Arkansas, 10
Arkansas Novaculite, 9
Askeaton, Eire, 61
Askrigg Block, 26
Assemblage Zones

Britain, 35-51

Germany, 52-63

U.S.A., 52-63 "
Auchenmade, 30

Australia, 11, 32, 53, 58, 60, 65, 178
Austria, 8
Avesnois, 9

Avon Gorge, 5, 6, 13, 17-18, 21, 32, 35-36,
39-41. 44. 46-4 8 . 5i. 53. 55-58. 60-62,
65-66, 78, 98, 106, 176, 193, 200, 202,
204, 205, 217, 244-56, 277
Avonia bassus, 17

Avonian, 13-15, 17-18, 55, 57, 61, 65, 158,

203, 206-207, 216, 228
Avonian sections, 13, 17-18, 24, 55
Avonian Zones, 59

conodont, 35

coral-brachiopod, 13-17
Ayrshire, 29, 30, 51, 244, 272-274, 277
Ayrshire Coalfield, 29
Aymestry Limestone, 6

Bactrognathus, 35, 60, 64-65

communis, 106
Bactrognathus — Polygnathus communis

Assemblage Zone, 56, 60
Bactrognathus — Taphrognathus Assemblage

Zone, 10, 56, 61
Barness East, 30, 50, 266
Barnett Formation, 10
Belgium, 9, 17, 36, 39-41. 52-54. 62-65
Berwick Formation, 60
Bilston Burn, 30, 269
Birdshill Limestone, 5
Bishopsteignton, 6
Bivalves, 13, 20
Black Lias Quarry, 23
Black Rock Limestone, 6, 17, 247
Black Rock Quarry, 21, 25
Brachiopods, 11, 13, 20, 27
Broadstone Limestone, 30, 51
Bollandian, 18
Bonaparte Gulf, 57-58
Boulonnais, 9
Breconshire, 66, 244
Bristol, 19, 22, 66, 228
Bryn Pig Limestone, 5
Bryozoa Bed, 20

Burlington Formation, 42, 57, 61, 64, 97, 277
Burrington Combe, 15
Bushberg — Hannibal, 9, 236
Bushberg Sandstone, 9, 56
B2 Zone, 18

Callington, 6

Calciferous Sandstone Measures, 4, 29, 30, 50

Calciferous Sandstone " Series ", 13, 18, 29,

270, 272
Caney Formation, 9
Caninia Oolite, 15, 18, 20, 22, 32, 61
Caninia Shales, 20
Caninia Zone, 15, 18, 20, 249, 250
Caradocian, 5

Carboniferous, Lower, 7-9, 11, 13, 19, 53, 243
Carboniferous Limestone Series, 23, 29, 30

306

BRITISH AVONIAN CONODONT FAUNAS

Carlops, 30, 50
Carmarthenshire, 5

Catcraig, 30

Cavusgnathus, 35, 43-44, 62, 77-78, 85, 150,
180, 219, 236, 242, 245

alia, 77, 78

char actus, 35, 43, 79-80, 83

convexus, 35, 50, 80-81, 83

cristatus, 43, 51, 80-81

regularis, 81

naviculus, 45, 50, 81-82, 84

unicornis, 35, 43-44, 82-84

? sp. nov. A, 84
Cavusgnathus unicornis — Apatognathus

libratus Zone, 43, 51, 61
Celloni Zone, 5
Cementstones, 13
Cementstone Group, 13, 29
Centrognathus spurius, 68
Cephalopod, 7, 9, 65
Chapel Hill Limestone, 10
Chapel Point, 30, 266
Chappel Limestone, 106, 203
Chester, 10, 45, 63

Chouteau Formation, 40-41, 55-57, 64, 277
Chudleigh, 6

Cladognathus primus, 130
Clee Hills, 25

Cleistopora Zone, 15, 20, 246, 261
Clevedonian, 15
Cleveland Hills, 7
Clifton, 21, 22
Clown Marine Band, 7

Clydagnathus , 4, 32, 53-54, 63, 84, 178-179,
219, 230, 236, 245

cavusformis, 32, 84-86, 88

darensis, 32, 41, 48, 86-87, 89

gilwernensis , 32, 36, 38, 48, 86, 87-88

sp. nov. A, 88-89

unicornis, 32, 40-41, 48, 88
Coal Farm, 30, 270
Coal Measures, 7
Colsterdale Marine Beds, 7
Concretionary Beds, 20, 22, 253
Conodonts, affinities of, 4

composition of, 4

function of, 5
Coral — brachiopod zones, 13-16, 20, 21
Cornbrook Sandstone, 25
Costatus Zone, 53
County Clare, 7
Cracoean, 18
Craigmore Ironstone, 7

Craig-y-Dinas, 23

Craven Lowlands, 13

Crinoids, 11, 20-21

Crtig Limestone, 5

Ctenognathus murchisoni, 222

Cu I Stage, 4, 11, 36, 39, 53-55, 65, 200, 203,

217
Cu I — Cu II Stages, 236, 277
Cu II Stage, 4, 9, 11, 39-43. 55-57. 59-62,

64-65. 150. 236, 277
Cu III Stage, 4, 44-45, 61-64, 277
Culm facies, 1 1
Cumberland, 6

Ci Subzone, 15, 18, 31, 42, 57, 62, 245, 277
C2S1 Subzone, 15, 18, 25, 43, 46, 277
C Zone, 15, 17, 22, 51, 60, 62, 65, 245

Dairy, 30

Dark Shale unit, 55

Derbyshire and Nottinghamshire Coalfield, 7

Devon, 18

Devonian, 5-8, 11, 53, 54, 77, 107, 126, 167,

178, 181, 200, 202, 222, 243
Devonian — Carboniferous boundary, 6, 54,

236
Dibunophyllum Zone, 15-16, 18, 23, 244, 254,

255. 256
Dinant Basin, 62
Dinantian, 9, 15, 17
Diplodella, no

Dockra Limestone, 30, 51, 272
Doliognathus, 35, 64-65
excavatus, 64
latus, 65
Drumbuie House, 30
Dryburn Foot, 30

Dunbar, 30, 45-50, 244, 264-266, 277
Durham, 26
Di Subzone, 4, 15, 17, 21, 25, 27, 44, 46, 62,

277
D2 Subzone, 4, 15, 17, 21, 23, 27, 44-46, 50,

62-63, 245, 259, 277
D3 Subzone, 4, 44-45, 50-51, 260, 277
D Zone, 15, 18, 22-23, 32, 42, 51, 61-62, 78,

149, 193, 196, 245, 254

East Germany, 8
East Ogwell, 6
Edenbrook Beds, 6
Edenork, 6
Eifelian, 6
Eire, 45

INDEX

3°7

Elictognathus, 35, 53, 54, 64

coslatus, 63
Ellisonia, no
Emsian, 6

England, South West, 6, 54
English River Formation, 9, 10
Eosteinhornensis Zone, 6
Erdbach Kalk, 8
Esneux, 53

Eumorphoceras Zone, 51
Euprioniodina, 89, 90

caverna, 90

deflecta, 89

microdenta, 91

sp. nov. A, 91, 92

sp., 92
Europe, western, 8
Ei Stage, 4, 18
Ejb Stage, 26
E2 Stage, 4, 18
E2a Stage, 62
E Zone, 62

Fall Bay, 61

Fammenian, 9, 53-54

Farlovian, 25

Farlow, 25, 48, 66, 244, 261, 277

Farlow Sandstones, 25

Fern Glen Formation, 9, 42, 60, 64, 97, 277

Fife, 29, 30, 45, 50, 52, 244, 270-271, 277

Fife Coalfield, 29

Fish Bed, 6

Fitzroy Basin, 178

Five Yard Limestone, 26-27, 45- 48. 263, 277

Foraminifera, n, 21, 54

France, 9, 52, 63, 64-65

Franco-Belgian Province, 9, 52, 64-65, 178

Frasnian, 6

Gastropods, n, 20

Gattendovfia Zone, 8, 17

Gayle Beck, 28, 262

Gayle Limestones, 26-27, 4^

Gelli-grin Limestone, 5

Gen. nov. A. sp., 242-243

Gen. nov. B. sp., 243

Geniculatus, 92

Germany, 4, 7-10, 40, 41, 44-45, 52, 54-57,

59, 62-65, 208, 243
Gilmerton Limestone, 30, 50, 267
Gilwern, 87
Girvanella Bed, 27
Givetian, 6

Glamorgan, Vale of, 22
Glenconse Burn, 30
Glen Dean Formation, 10, 45, 63
Glengarnock, 30, 51, 277
Glen Park Formation, 55, 217
Glonbeith Castle, 30
Gloucestershire, n
Gnathodids, 34, 41-43
Gnathodus, 34, 56-58, 93, 245

antetexanus, 34, 40-42, 48, 56-57, 60, 64,

93-94, 98
avonensis, 34, 41, 94

bilineatus, 34, 44-46, 51, 62-64, 94~95> 99
bilineatus — Cavusgnathus charactus

Assemblage Zone, 10, 63
cf. girtyi, 64

commutatus, 34, 45, 51, 64, 95-96, 104-105
cuneiformis, 34, 43, 64, 97, 206
delicatus, 34, 39-41, 56-57, 64, 97-98, 277
girtyi, 50-51, 57, 61, 63-64, 99-102, 109
girtyi collinsoni, 34, 45, 48, 51-52, 63,

99-100
girtyi collinsoni Assemblage Zone, 48,

50-51, 63, 277
girtyi Form A, 62, 102
girtyi Form B, 62
girtyi Form C, 63

girtyi girtyi, 34, 44, 45, 51, 62, 98, 100-102
girtyi simplex, 34, 44-45, 51, 62
girtyi soniae, 101-102
girtyi turritns, 34, 45, 48, 50-51, 102
homopunctatus, 34, 44-45, 48, 62-64, io 3>

108
kockeli, 53, 55
kockeli — Pseudopolygnathus dentilineatus

Zone, 8, 54-55
mononodosus, 34, 44-45, 48, 50-51, 63,

103-105
mononodosus Assemblage Zone, 45, 48, 50,

63. 277
mosquensis, 93

nodosus, 45, 51, 63, 94, 104-105
punctatus , 34, 60, 105-106
semiglaber , 34, 40-42, 56-57, 60, 62, 64, 98,

106-107
semiglaber — Pseudopolygnathus multi-

striatus Assemblage Zone, 10, 56, 59-60
simplicatus, 34, 40-41, 64, 94, 107-108
symmutatus, 44, 103-104, 108
? sp. nov., 109
sp, 109

sp. n. B — Gnathodus kockeli Assemblage
Zone, 55

3 o8

BRITISH AVONIAN CONODONT FAUNAS

texanns, 42, 61-62, 206
Golconda Group, 10
Goniatites Zone, 13, 18, 26, 52, 54
Gower, 18, 22, 61, 244
Gramscatho Limestone, 6
Grassington, 26
Grassy Creek, 236
Great Quarry, 22, 251-252
Great Scar Limestone, 26

Hainault, 9

Hangenberg Limestone, 17

Hangenberg Schiefer, 8

Hannibal Formation, 9, 36, 39-40, 53-56, 60,

200, 217
Hannibal — Upper Chouteau, 277
Harden Burn, 30, 51, 275
Hardraw Scar Limestone, 26-28, 48, 277
Hartz Mountains, 64
Hassognathus, 111
Hastiere Limestone, 17
Hibbardella, 110-111
Hibbardella (Hassognathus) 117
Hibbardella {Hibbardella) abnormis, 44,

IIO-III

acuta, 112

miller i, 113

ortha, 113-115

parva, 11 4-1 15

cf. macrodentata, 115, 117

separata, 117

sp., 115-116

? sp., 117
Hibbardella (Prioniodus) angulata, 110-111
Hindeodella, 118

antecomplex , 35, 118-119

brevis, 119

cooperi, 120-123

corpulenta, 35, 39, 120-121, 243

croka, 121

hibbardi, 122

ibergensis, 123

montanaensis , 123-124

secarata, 124

segaformis, 64-65

subtilis, 35, 40, 118, 125-126

tenuis, 126-127

undata, 35, 127

sp., 127

sp. nov., 128
Hindeodus, 128

alaloides, 129

imperfectus, 129, 130

sp., 130
Honnetal, 54
Hosie Limestone, 30, 51, 271, 273

Lower, 51-52, 271

Middle, 51-52, 271

Upper, 271
Hurlet Limestone, 51-52, 270-271
Hiiy, 54

Illinois Basin, 10, 56

Index Limestone, 30, 51, 274

Indiana, 10, 59

Intercontinental correlation, 36

Intra-Avonian unconformity, 245

Ireland, 11, 13, 45

Iowa, 9-10, 63

Keisley Limestone, 5

Kentucky, 10

Keokuk Formation, 9-10, 43, 277

Kidwellian, 15

Kilsyth, 6

Kinderhookian Series, 59, 98

Kinkaid Formation, 10

Kladognathus , 35, 130-132

-Cavusgnathus naviculus Assemblage Zone,
10

clarensis, 131

macro dentatus , 132

mehli, 132
K Zone, 4, 15, 17-18, 20-21, 25, 31-33, 36,
39-40, 46, 48, 52-53, 55-56, 59, 63,
78, 86, 200-203, 217, 221, 244, 245-246,
257, 261, 277
" Lagoon " facies, 11

Laminosa Dolomites, 16, 20, 22, 31-32, 60-61
Lancashire, 7
Landelies Limestone, 17
Legend for lithological sections, 276
Leicestershire and South Derbyshire

Coalfield, 7
Leigh Woods, 21-22
Leinster, 11
Ligonodina, 118, 133, 145

beata, 35, 39, 48, 133, 139

clarki, 143

complectens, 132

levis, 45, 134, 135

magnilaterina, 135-136

osborni, 136-137

pectinata, 133

roundyi, 137-138

tenuis, 138

INDEX

309

lulensis, 139

sp. A, 139

sp., 139, 140

? sp., 139, 140
Lilleshall, 25
Limestone III A, 27

III B, 27

III C, 27

IV A, 27
IV B, 27

IV C, 26-27

V A, 26-27

VI A, 26-27
VI B, 26-27

Limestone Coal Group, 18, 29-30
Linn Limestone, 30

Lower, 30, 51

Upper, 30, 51, 274
Linn Spout, 30, 51
Little Wenlock, 25
Llandeilian, 5
Llandeilo Limestone, 5
Llandovery, 5
Llanelli Quarry, 25
Lodgepole Limestone, 55
Lonchodina, 140

bolbosa, 140

furnishi, 141, 142

obtunda, 142

paraclarki, 143

paraclaviger, 143-144

transitans, 144

typicalis, 140

sp. A, 144
Long Craig Limestone, Upper, 30, 50, 264
Louisiana Limestone, 53, 222, 236
Lower Limestone Group, 4, 18, 29-30, 50-51,

264-269, 271-273
Lower Limestone Shale, 6, 13, 17, 36, 54

Machrihanish, 30
Macropolygnathns, 201

ithus, 201
Magnilaterella, 51, 132, 135, 144-148

clarkei, 35, 146-147

complectens , 145-146

contraria sp. nov., 147-148

robusta, 144, 148

sp., 149

spp., 149

? sp., 149, 150
Main Limestone, 26
Malvern Hills, 5

Marble Cliff Beds, 6
Marbre Noir Series, 17
Maury Shale, 10
McCraney Limestone, 10
Mellte Bridge, 23
Melmerby Scar Limestone, 26
Menard Formation, 10-11
Merocanites, 18

Mestognathus, 35, 51, 57, 61, 78, 150-152,
180, 219

beckmanni, 42-45, 61-63, J 5°

beckmanni — Gnathodus bilineatus Zone, 44,
63

bipluti, 35, 44-45, 152-153

neddensis, 35, 45, 153, 154
Metalonchodina, 131, 154

bidenlata, 154-156
Middle Limestone, 26-27, 4^. 277
Midland Coalfields, 7
Midland Valley, Scotland, 4, 13, 29, 66
Midlothian, 150, 244, 267-269, 277
Millstone Grit, 7, 22, 26
Milston Bridge, 30
Mississippian, 9-10, 55, 200, 217
Mississippi Valley, 4-5, 10-11, 36, 41, 44-45,

52-53. 55. 57-63. 77, 217. 277
Missouri, 9, 56, 59
Modiola phase, n, 15
Monmouthshire, 66, 244
Montana, 9, 11, 55, 179
Montfort, 53
Muensteroceras, 18, 60

inconstans , 18
Mullion Island, 6
Mumbles, 23

Namurian, 4, 7, 18, 45, 62, 177
Neal Point, 6
Neoprioniodus, 90, 156

antespathatus , 156, 157

cf. armatus, 167

barbatus, 40, 158

cf. camurus, 167

confluens, 158-159

conjunctus, 159-160

montanaensis , 44, 160-161

peracutus, 35, 161-162

scitulus, 35, 45, 162-163, ID 5

spathatus, 163-164

tulensis, 45, 164-165

varians, 165-166

sp. nov. A, 166-167
Newhall House, 30

3'°

BRITISH AVONIAN CONODONT FAUNAS

Now Providence Shale, 56, 59
Non Calcareous Measures, 27
North Crop (see South Wales Coalfield)
North Greens Limestone, 30, 268
North Scar Gill, 28
North Staffordshire, 7
Northumberland, 13, 26
Northumbrian Trough, 13

Octoplicata Shale, 17

Oil Shales, 13

Oil Shale Group, Lower, 29

Oklahoma, 9, 56, 59

Old Red Sandstone, 18

Ordovician, 5

Oreton, 25, 244

Oreton Quarry, 262

Osage series, 59

Ostracods, 11, 13, 20

Ozarkodina, 168, 195

compressa, 169-170, 173

curvata, 168-169

delicatula, 1 70-1 71

cf. delicatula, 177

cf. elegans, 177

hindei, 1 71-173

macer, 173

macra, 174

parva, 174-175

plana, 175

plnmula, 175-176

cf. congesta, 176

sp., 178

Palaeogeography — British Carboniferous, 12
Palate Bed, 20
Palmatolepis , 53

glabra subsp. indet., 53, 179

gracilis, 53
Paoli Formation, 10
Paraconodonts, 5
Passage Group, 29
Patrognathus, 4, 32, 54, 63, 87, 178, 245

variabilis, 36, 46, 48, 52, 87, 178, 179
Patrognathus variabilis — Spathognathodus

plumulus Assemblage Zone, 36, 48
Pelecypods, 11
Pella Formation, 10, 63
Pembrokeshire, 22, 244
Pendleian, 18
Pennsylvanian, 7, 177
Pentamerus Beds, 5
Pen-y-garnedd Limestone, 5

Peracuta Shale, 17
Pericyclus kochi, 18

princeps, 9, 65
Pericyclus Stage, 8
Phragmodus, 136
Pierson Formation, 59
Pilton Beds, 6, 54
Pittenweem, 30
Plectospathodus, 18 1

? sp. A, 181

sp. B, 181
Polygnathus, 34, 62, 182, 213, 245

bischoffi, 35, 42, 61, 184-185

? claviger, 92

communis, 34, 40, 48, 60-61, 64

communis communis, 42, 182, 183, 184

fusiformis, 201

inornatus, 35, 39, 46, 48, 63, 185

inornatus inornatus, 34, 36, 38, 48, 57,
185-186, 192

inornatus rostratus, 34, 38, 48, 186-187

inornatus vexatus, 35, 187, 188

lacinatus, 35, 41, 46, 51, 60, 62, 185, 188

lacinatus asymmetricus , 35, 41, 188

lacinatus circaperipherus , 189

lacinatus lacinatus, 35, 41—42, 189-191

lacinatus prelobatus , 190-191

lacinatus Zone, 41, 57, 59, 277

lobalus lobatus, 34, 36, 38, 48, 185, 191-192

lobatus inflexus, 35, 38, 192

macrus, 211

nodomarginatus, 55

orthus, 221

sp., 192, 193
Portishead Beds, 17
Portugal, 8

Pre-Welden Shale Formation, 56
Prioniodina, 90, 193-194, 197

eireica, 194-196

laevipostica, 35, 195-197

latericrescens, 196

oweni, 196-197

prelaevipostica, 197

stipans, 45, 198

subaequalis, 45, 198-199

subcurvata, 90, 194

? sp. nov., 199, 200
Prolecanites discoides, 18
Prospect Hill Siltstone, 9, 10
Protocanites, 18, 60
Pseudobreccias, 22, 27

Pseudopolygnathus, 32-34, 40, 42, 55, 180,
200, 204, 207, 213, 226, 236, 239, 245

INDEX

3ii

apetodus, 203-204

attenuatus, 212

dentilineatus , 32, 40-41, 54, 63, 65, 203,

208-209, 212, 215-217
expansus, 32, 209-210, 217
foliacens, 203
cf. fusiformis, 210
lacinatus, 42, 213
lanceolatus , 206, 212
cf. longiposticus, 34, 41-42, 46, 206,

210-212
multistriatus , 34, 40-41, 46, 60, 65, 202,

206, 211-212, 216
nodomarginatus , 32, 41, 212
primus, 32, 40-41, 200-204, 2 °°, 2 °9. 2I °.

212, 214-216
postinodosus, 32, 40, 213, 214, 239
striatus, 206, 209, 212
symmetricus , 55

triangulus inaequalis , 64-65, 203, 206
triangulus pinnatus, 60-61, 216
triangulus subsp. indet, 203
triangulus triangulus, 60, 203, 206
sp., 54, 214, 218
vogesi, 32-33, 36, 38, 46, 54, 202, 210,

216-217
vogesi — Clydagnathus Assemblage Zone

54-55
Pi Stage, 18, 44-45, 62
Pic Stage, 26
P 2 Stage, 18, 62

Quarry I, 21, 246-247
Quarry 2, 22, 247-248
Quarry 3, 22, 249
Quarry 4, 22

Rheinisches Schiefergebirge, 18

Rhenaer Kalk, 63

Rhenoherzynicum, 8

River Clydach, 24, 84, 86

River Mellte, 23

River Nedd, 23, 153

River North Esk, 30

River Sychryd, 23

Rockford Limestone, 10, 56, 59

Rossmore Beds, 6

Roundya, 110-111, 116, 139

barnettana, 111, 116

sp., 116-117
Roxburghshire, 30, 51, 244, 275, 277
Rib Stage, 26

Salem Formation, 10, 43, 62
Sauerland, 64, 203
Saunton, 6
Saverton Shale, 53
Scaliognathus , 35, 64-65

anchoralis, 8, 9, 64-65

anchoralis — Gnathodus bilineatus
' interregnum ", 8

anchoralis Zone, 64
Scaphignathus, 53, 84-85, 178, 180, 218, 230

veliferus, 53, 218

? sp. A, 218

? sp. B, 219
Scotland, 5, 18, 29, 36, 49, 50-52, 62, 66, 244,

277
Sedalia Formation, 41, 59, 60, 64, 97, 277
Seminula Zone, 15-16, 18, 20, 251, 252, 253
Shale Group, Upper, 29
Shirehampton Beds, 6, 17
Shropshire, 5, 6, 25, 32, 66, 244-245, 261,

262, 277
Siegenian, 6
Silurian, 5, 6, 181
Siphognathus duplicatus, 219
Siphonodella, 32, 36, 46, 53, 55, 57-59, 64,
185, 219, 222, 236, 245

cooper i, 106

crenulata Zone, 8, 55, 60, 64

duplicata, 63-64

isosticha, 38-39, 55, 57, 220-221

isosticha — 5. cooperi Assemblage Zone, 10,

5&-57. 59
lobata, 63

obsoleta, 63-64, 220-221
— Polygnathus inornatus Assemblage Zone,

38, 55. 57
— Pseudopolygnathus triangulus inaequalis

Zone, 8
— Pseudopolygnathus triangulus triangulus

Zone, 8, 55
quadruplicata, 63
— quadruplicata — 5. crenulata Assemblage

Zone, 55-56
sexplicata, 63
sp. A, 221
sp., 221
Subzone, 4, 55
sulcata, 54, 55

sulcata Assemblage Zone, 54
triangulus triangulus Zone, 55
zones of Mississippi Valley, 59
Simonstone Limestone, 26-27, 45> 4^.

262-263, 2 77

3»=

BRITISH AVONIAN CONODONT FAUNAS

Skateraw, Lower, 30, 50, 265
Middle, 30, 50
Upper, 30, 265
Skipsey's Marine Band, 7
Snaizeholme Valley, 28, 263
Somerset, 6, 1 1
South Dakota, 1 1
South Staffordshire, 6
Southern Uplands, 1 1

South Wales Coalfield, North Crop, 22-24,

32-33, 35-36, 39, 40-41, 44-48, 50-51,

54. 5 6 . 58, 63, 66, 95, 102, 193, 200,

244-245, 257-60, 277

South West Province, 4, 6, 11, 13, 48, 56, 62,

244-245, 277
Spain, 64-65

Spathognathodus, 33-34, 200, 209, 221-245
aculeatus, 53-54, 200, 230, 236-237
anleposicornis, 34, 39, 200, 222-223, 2 3 I >

236-237
bidentatus, 107
bischoffi, 204, 223, 236, 239
cf. campbelli, 34, 233
cf. cristulus, 34, 39, 40-42, 48, 233-234
cf. robustus, 34, 39, 48, 235, 240
chouteanensis, 229, 231, 235
coaptus, 224, 225
costatus, 53-54, 59, 202, 236
costalus costatus, 33-34, 39-41, 46, 48, 202,

204, 225-226, 236-237
costatus costatus — Gnathodus delicatus

Assemblage Zone, 39, 40, 48, 56-57, 277
costatus (spinulicostatus) ultimus, 202, 236
costatus sulciferus, 33-34, 39, 40-41, 200,

226, 236
costatus sulciferus — Gnathodus delicatus

Assemblage Zone, 56
costatus Zone, 53, 55, 59
crassidentatus, 33-34, 39, 41, 48, 225-227,

229, 231, 235, 240
cristulus, 34, 43, 45, 107, 227, 234
cyrius, 33-34, 39, 227, 234
denticulatus , 225, 229
elongatus, 33-34, 39, 48, 228-229, 231
plumulus, 34, 54, 79, 230-231
plumulus plumulus, 33, 36, 39, 46, 53, 85,

200, 229, 230-231, 236
plumulus nodosus, 33, 38, 230
plumulus shirleyae, 33, 36, 230-231
pulcher, 34, 41, 231
regularis, 234
robustus, 46, 235

robustus — S. tridentatus Assemblage Zone,

39, 48, 55- 277

scitulus, 34, 44, 232

scitulus subsp. A, 232

sp. A, 239, 240

sp. B, 240

spinulicostatus , 202, 230, 236

spinulicostatus ultimus, 202

sp. nov., 240, 241

stabilis, 231

sulciferus, 230, 235

tridentatus, 33-34, 39, 41, 48, 206, 230,
2 3i> 235, 236-237

ziegleri sp. nov., 236, 238, 239
Spores, 54

Staurognathus , 35, 64-65
St. Genevieve Formation, 10, 44, 63
St. George's Land, 1 1
St. Louis Limestone, 10, 63
St. Louis Formation, 43, 44, 62, 77, 277
St. Mellion, 6
Sublaevis Beds, 17
S2 Subzone, 15, 20, 22, 25, 42-44, 46, 62, 245,

258, 277
S Zone, 15, 17, 22, 32, 42-43, 61-62, 245, 251
Summary, 52
Synprioniodina, 90

Tamar Valley, 6

Tanhouse Beds, 18

Taphrognathus, 35, 43, 62-63, 7$. 85, 178,
241-242, 245
varians, 35, 43-44, 51, 62, 241-242
varians — Apatognathus Assemblage Zone,

10, 61-62
varians — Cavusgnathus — Apatognathus
Zone, 43, 61

Teesdale, 26

Tennessee, 10

Texas, 203

Thorny Force Sandstone, 27

Three Cliffs Bay, 18

Three Yard Limestone, 26, 28, 45

Titterstone Clee Hill, 25

Tm Stage, 53

Tn la Stage, 53, 63

Tnn,/Tn2b Stages, 178

Tn 2 b Stage, 36, 63

Tn 2c Stage, 36, 39-40. 63

Tn 3a Stage, 40, 63-65

Tn 3 b Stage, 9, 41, 42, 64-65

Tn 3c Stage, 9, 42, 45

Tonge's Marine Band, 7

INDEX

3i3

Top Hosie Shale, 6

Torquay, 6

Tournaisian, 6, 9, 15, 17, 52, 54, 63, 65, 126,

178
Tournaisian — Visean boundary, 17, 65
Trichognathus separatus, 1 1 1
Trichonodella, no, 130

imperfecta, 128
Tyrone, 6

Unconformity, 64, 245, 277

Underset Limestone, 26, 28, 45, 263

United States, 60, 65, 243

Upper Limestone Group, 4, 18, 29, 30, 51,

274
Usk, 6

Valmeyeran Series, 45, 62, 78, 98
Vaughan's coral — brachiopod zones, 13-15,

17. 245
Vexhim Limestone, 30, 50
VI Zone, 54
Virginia, 10

Visean, 9, 15, 17-18, 45, 52, 63, 77, 126, 177
Viverdon Down, 6

Wales, 5, 11

Warsaw Formation, 10, 43, 62

Wassonville Dolomite, 10

Waterlip Quarry, 6

Welsh Borderland, 6

Wenlock Limestone, 6

Wensleydale, 26, 28

Western Australia, Canning Basin of, 53

Western Europe, 43, 52, 54-55, 60-62
West Germany, 15, 36, 39, 52-53, 55, 61,

200, 217
Westmorland, 5
Westphalian, 25
West Virginia, 10
Wilsoni Shales, 5
Windsor Hill, 6

Windy Gap Formation, 54, 179
Whitcliffe Flags, 6
Whitcliffian Limestone, 6
White River, 59
Wocklumeria, 8
Wocklumeria Stage, 54, 202
Wocklumeria — VI Zone, 54
Woolhope Inlier, 5, 6
Wyoming, 11, 54-55, 179

Yate, 18

Yoredale Formation, 6, 25, 27-28, 45,

244, 262-263, 2 77
Yorkshire, 5, 6, 25, 102, 244, 277

\, 62,

Zaphrentis Zone, 15, 16, 247, 262

Zi Subzone, 15, 21, 60, 64, 203-205

Z2 Fish Bed, 65

Z2 Limestone, 22

Z2 Subzone, 15, 57, 60, 62, 64, 98, 106,

205-206, 277
Z Zone, 17, 18, 20, 22, 31-33, 39-40, 42, 46,

48, 52. 55-56, 60, 65, 78-79, 158, 176,

200, 202, 209, 216, 244-245, 247, 248,

258, 262, 277

PLATES

PLATE i
All specimens coated and magnified X 31.5

Figs, i, 2, 5, 6. Spathognathodus plumulus plumulus sp. nov.

ia. Outer lateral view of holotype X 476. ib. Oral view of holotype X 476. ic. Aboral
view of holotype X 476. 2a. Outer lateral view of paratype X 379. 2b. Oral view of paratype
X 379. 2c. Aboral view of paratype X 379. 5. Outer lateral view of paratype X 380,
posterior portion missing. 6. Outer lateral view of juvenile paratype X 381, anterior aboral
portion of blade missing.

Figs. 3,4. Spathognathodus plumulus nodosus subsp. nov.

3a. Outer lateral view of paratype X 383, posterior portion missing. 3b. Oral view of paratype
X 383- 3c. Aboral view of paratype X 383. 4a. Outer lateral view of holotype X 382,
posterior portion missing. 4b. Oral view of holotype X 382. 4c. Aboral view of holotype
X 382.

Figs. 7, 8. Spathognathodus plumulus shirleyae sp. et subsp. nov.

7a. Outer lateral view of paratype X 385, posterior portion missing. 7b. Oral view of paratype
X 385. 8a. Outer lateral view of holotype X 384. 8b. Oral view of holotype X 384. 8c.
Aboral view of holotype X 384.

Figs. 9-13. Clydagnathus cavusformis gen. et sp. nov.

9. Oral view of paratype X 72. 10. Oral view of paratype X 73. 11a. Outer lateral view of
holotype X 75. 11b. Inner lateral view of holotype X 75. 11c. Oral view of holotype X 75.
1 id. Aboral view of holotype X 75. 12a. Outer lateral view of paratype X 71. 12b. Inner
lateral view of paratype X 71. 12c. Oral view of paratype X 71. i2d. Aboral view of para-
type X 71. 13a. Outer lateral view of paratype X 74, posterior portion missing. 13b. Inner
lateral view of paratype X 74. 13c. Oral view of paratype X 74. 13d. Aboral view of
paratype X 74.

Bull. Br. Mus. nal. Hist. (Geol. Suppl.) 5

PLATE 1

PLATE 2
All specimens coated and magnified x 31.5

Fig. 1. Clydagnathus gilwernensis gen. et sp. nov.

a. Oral view of holotype X 78. b. Outer lateral view of holotype X 78.
view of holotype X 78. d. Aboral view of holotype X 78.

c. Inner lateral

Figs. 2, 3, 5. Clydagnathus unicornis gen. et sp. nov.

2a. Oral view of holotype X 79. 2b. Outer lateral view of holotype X 79. 2c. Inner lateral
view of holotype X 79. 2d. Aboral view of holotype X 79. 3a. Oral view of paratype X 80.
3b. Outer lateral view of paratype X 80. 3c. Inner lateral view of paratype X 80. 3d. Aboral
view of paratype X 80. 5a. Oral view of paratype X 81. 5b. Inner lateral view of paratype
X 81.

Fig. 4. Clydagnathus gen. et sp. nov. A

a. Oral view of specimen X 82. b. Outer lateral view of specimen X 82. c. Inner lateral
view of specimen X 82. d. Aboral view of specimen X 82.

Figs. 6, 7. Clydagnathus darensis gen. et sp. nov.

6a. Oral view of holotype X 77. 6b. Outer lateral view of holotype X 77. 6c. Inner lateral
view of holotype X 77. 6d. Aboral view of holotype X 77. 7a. Oral view of paratype X 76.
7b. Outer lateral view of paratype X 76. 7c. Inner lateral view of paratype X 76. 7d. Aboral
view of paratype X 76.

Figs. 8-1 i. Patrognathus variabilis gen. et sp. nov.

8a. Oral view of paratype X 310. 8b. Lateral view of paratype X 310. 9a. Oral view of
paratype X 519. 9b. Aboral view of paratype X 519. 9c. Lateral view of paratype X 519.
10a. Oral view of paratype X 309. 10b. Aboral view of paratype X 309. ioc, Lateral view
of paratype X 309. 11 a. Oral view of holotype X 311. 11b. Aboral view of holotype X 311.
iic. Lateral view of holotype X 311.

Fig. 12. Scaphignathus ? sp. B

a. Oral view of specimen X 533. b. Inner lateral view of specimen X 533. c. Aboral view
of specimen X 533.

Fig. 13. Scaphignathus ? sp. A

a. Oral view of specimen X 532. b. Inner lateral view of specimen X 532. c Aboral view
of specimen X 532.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 2

PLATE 3
All specimens coated and magnified X 31.5

Figs. 1-4. Spathognathodus crassidentatus (Branson & Mehl)

ia. Inner lateral view of specimen X 463. ib. Aboral view of specimen X 463. 2a. Inner
lateral view of specimen X 460. 2b. Oral view of specimen X 460. 3a. Inner lateral view of
specimen X 461. 3b. Aboral view of specimen X 461. 4a. Inner lateral view of specimen
X 462. 4b. Aboral view of specimen X 462.

Figs. 5-8. Spathognathodus anteposicornis Scott

5a. Inner lateral view of specimen X 540. 5b. Oral view of specimen X 540. 6a. Inner
lateral view of specimen X 543. 6b. Aboral view of specimen X 543. 7a. Inner lateral view
of specimen X 541. 7b. Aboral view of specimen X 541. 8a. Inner lateral view of specimen
X 542. 8b. Oral view of specimen X 542.

Figs. 9-12. Spathognathodus tridentatus (E. R. Branson)

9a. Inner lateral view of specimen X 395. 9b. Oral view of specimen X 395. 9c. Aboral view
of specimen X 395. 10a. Inner lateral view of specimen X 396. 10b. Oral view of specimen
X 396. ioc. Aboral view of specimen X 396. 11a. Inner lateral view of specimen X 397.
11b. Oral view of specimen X 397. 11c. Aboral view of specimen X 397. 12a. Inner lateral
view of specimen X 394. 12b. Oral view of specimen X 394. 12c. Aboral view of specimen
X 394-

Figs. 13-15. Spathognathodus costatus costatus (E. R. Branson)

13a. Inner lateral view of specimen X 456. 13b. Aboral view of specimen X 456. 14a. Inner
lateral view of specimen X 166. 14b. Oral view of specimen X 166. 15a. Inner lateral view
of specimen X 455. 15b. Oral view of specimen X 455.

Figs. 16-18. Spathognathodus costatus sulciferus (Branson & Mehl)

16a. Inner lateral view of specimen X 459. 16b. Oral view of specimen X 459. 17a. Inner
lateral view of specimen X 458. 17b. Aboral view of specimen X 458. 17c. Oral view of
specimen X458. 18a. Aboral view of specimen X 457. 18b. Inner lateral view of specimen
X 457. 18c. Oral view of specimen X 457.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 3

J^^^k i^HWrfil il ^ ^JMl A i fcHtmrirff i^ l l

la 2a 3 a 4a

2b 3b 4b

mm* **4k tfntui *ma

5a 6a 7a "^ 8a

11a 12a

♦ «»•

PLATE 4
All specimens coated and magnified X 31.5

Figs. 1-4. Spathognathodus bischoffi sp. nov.

ia. Oral view of paratype X 399. ib. Aboral view of paratype X 399. ic. Outer lateral view
of paratype X 399. id. Inner lateral view of paratype X 399. 2a. Oral view of paratype
X 400. 2b. Aboral view of paratype X 400. 2c. Outer lateral view of paratype X 400.
2d. Inner lateral view of paratype X 400. 3a. Oral view of paratype X 398. 3b. Aboral
view of paratype X 398. 3c. Outer lateral view of paratype X 398. 3d. Inner lateral view of
paratype X 398. 4a. Oral view of holotype X 401. 4b. Aboral view of holotype X 401.
4c. Outer lateral view of holotype X 401. 4d. Inner lateral view of holotype X 401.

Figs. 5-8. Spathognathodus ziegleri sp. nov.

5a. Oral view of paratype X 437. 5b. Aboral view of paratype X 437. 5c. Outer lateral
view of paratype X 437. 5d. Inner lateral view of paratype X 437. 6a. Oral view of paratype
X 402. 6b. Aboral view of paratype X 402. 6c. Outer lateral view of paratype X 402.
6d. Inner lateral view of paratype X 402. 7a. Oral view of paratype X 404. 7b. Aboral
view of paratype X 404. 7c. Outer lateral view of paratype X 404. 7d. Inner lateral view
of paratype X 404. 8a. Oral view of holotype X 403. 8b. Aboral view of holotype X 403.
8c. Outer lateral view of holotype X 403. 8d. Inner lateral view of holotype X 403.

Figs. 9-1 1. Spathognathodus pulcher Branson & Mehl

9a. Oral view of specimen X 386. 9b. Aboral view of specimen X 386. 9c. Lateral view of
specimen X 386. 10a. Oral view of specimen X 513. 10b. Aboral view of specimen X 513.
ioc. Lateral view of specimen X 513. 10c. Lateral view of specimen X 513. 11a. Oral
view of specimen X 512. lib. Aboral view of specimen X 512. 11c. Lateral view of specimen
X512.

Fig. 12. Spathognathodus sp. A

a. Oral view of specimen X 405. b. Aboral view of specimen X 405. c. Lateral view of
specimen X 405.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 4

PLATE 5
All specimens coated and magnified X 31.5

Figs, i, 3, 5-8. Pseudopolygnathus vogesi sp. nov.

ia. Aboral view of holotype X 155. ib. Oral view of holotype X 155. ic. Lateral view of
holotype X 155. 3a. Aboral view of paratype X 504. 3b. Oral view of paratype X 504.
3c. Lateral view of paratype X 504. 5a. Oral view of paratype X 507. 5b. Aboral view
of paratype X 507. 5c. Lateral view of paratype X 507. 6a. Oral view of paratype X 505.
transitional to Ps. expansus. 6b. Aboral view of paratype X 505. 6c. Lateral view of paratype
X 505. 7a. Aboral view of paratype X 501. 7b. Oral view of paratype X 501. 8a. Aboral
view of paratype X 506. 8b. Oral view of paratype X 506.

Figs. 2, 4. Pseudopolygnathus expansus sp. nov.

2a. Aboral view of paratype X 482. 2b. Oral view of paratype X 482. 2c. Lateral view of
paratype X 482. 4a. Oral view of holotype X 483. 4b. Aboral view of holotype X 483.
4c. Lateral view of holotype X 483.

Figs. 9-13. Pseudopolygnathus dentilineatus E. R. Branson

9a. Aboral view of juvenile specimen X 478. 9b. Oral view of juvenile specimen X 478.
9c. Lateral view of juvenile specimen X 478. 10a. Aboral view of juvenile specimen X 477.
10b. Oral view of juvenile specimen X 477. 10c. Lateral view of juvenile specimen X 477.
11a. Oral view of specimen transitional from Spathognathodus X 479. 11b. Aboral view of
specimen transitional from Spathognathodus X 479. 11c. Lateral view of specimen transitional
from Spathognathodus X 479. 12a. Aboral view of specimen X 480. 12b. Oral view of
specimen X 480. 12c. Lateral view of specimen X 480. 13a. Aboral view of adult specimen
X 481. 13b. Oral view of adult specimen X 481. 13c. Lateral view of adult specimen
X481.

Figs. 14-16. Pseudopolygnathus multistriatus Mehl & Thomas

14a. Oral view of specimen X 486. 14b. Aboral view of specimen X 486. 14c. Lateral view
of specimen X 486. 15a. Aboral view of specimen X 487. 15b. Oral view of specimen X 487.
15c. Lateral view of specimen X 487. 16a. Oral view of specimen X 485. 16b. Aboral view
of specimen X 485. 16c. Lateral view of specimen X 485.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 5

PLATE 6
All specimens coated and magnified X 31.5

Fig. 1. Pseudopolygnathus cf. fusiformis Branson & Mehl
a. Aboral view of specimen X 552. b. Oral view of specimen X 552.

Fig. 2. Pseudopolygnathus multistriatus Mehl & Thomas

a. Oral view of specimen X 484. b. Aboral view of specimen X 484. c. Lateral view of
specimen X 484.

Fig. 3. Pseudopolygnathus sp. A.

a. Oral view of specimen X 515. b. Aboral view of specimen X 515. c. Lateral view of
specimen X 515.

Figs. 4, 5, 7, 10-12. Pseudopolygnathus primus Branson & Mehl

4a. Aboral view of specimen X 546. 4b. Oral view of specimen X 546. 4c. Lateral view of
specimen X 546. 5a. Aboral view of specimen X 497. 5b. Oral view of specimen X 497.
7a. Aboral view of specimen X 499. 7b. Oral view of specimen X 499. 7c. Lateral view of
specimen X 499. 10a. Aboral view of specimen X 500. 10b. Oral view of specimen X 500.
ioc. Lateral view of specimen X 500. 11a. Aboral view of specimen X 549. 11b. Oral view
of specimen X 549. uc. Lateral view of specimen X 549. 12a. Aboral view of specimen
X 498. 12b. Oral view of specimen X 498. 12c. Lateral view of specimen X 498.

Fig. 6. Pseudopolygnathus postinodosus sp. nov.

a. Aboral view of holotype X 496. b. Oral view of holotype X 496. c. Lateral view of
holotype X 496.

Fig. 8. Pseudopolygnathus dentilineatus E. R. Branson

a. Aboral view of specimen X 438. b. Oral view of specimen X 438. c. Lateral view of
specimen X 438.

Fig. 9. Spathognathodus sp. nov.

a. Oral view of specimen X 518. b. Aboral view of specimen X 518. c. Lateral view of
specimen X 518.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 6

TLATE 7
All specimens coated and mangified X 31.5

Figs. 1-5. Spathognathodus elongatus (Branson & Mehl)

ia. Lateral view of specimen X 472. ib. Oral view of specimen X 472. 2. Lateral view of
specimen X 474. 3. Aboral view of specimen X 472. 4a. Lateral view of specimen X 473.
4b. Aboral view of specimen X 473. 5a. Lateral view of specimen X 475. 5b. Aboral view
of specimen X 475.

Figs. 6, 7. Spathognathodus cf. robustus (Branson & Mehl)

6a. Lateral view of specimen X 388. 6b. Oral view of specimen X 388. 6c. Aboral view of
specimen X 388. 7a. Lateral view of specimen X 387. 7b. Oral view of specimen X 387.
7c. Aboral view of specimen X 387.

Fig. 8. Spathognathodus sp. B

a. Lateral view of specimen X 406. b. Oral view of specimen X 406. c. Aboral view of
specimen X 406.

Figs. 9-1 i. Spathognathodus coaptus (Branson & Mehl)

9a. Lateral view of specimen X 454. 9b. Aboral view of specimen X 454. 9c. Oral view of
specimen X 454. 10a. Lateral view of specimen X 453. 10b. Aboral view of specimen X 453.
toe. Oral view of specimen X 453. 11a. Lateral view of specimen X 436. lib. Aboral view
of specimen X 436. 11c. Oral view of specimen X 436.

Figs. 12-14. Spathognathodus cf. cyrius (Cooper)

12a. Lateral view of specimen X 471. 12b. Oral view of specimen X 471. 12c. Aboral view
of specimen X 471. 13a. Lateral view of specimen X 470. 13b. Oral view of specimen
X 470. 13c. Aboral view of specimen X 470. 14a. Lateral view of specimen X 469. 14b.
Oral view of specimen X 469. 14c. Aboral view of specimen X 469.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 7

■"'■'"Hirf* rfT'imflfa wawafarift

1 n A ~

<$&tifk tfUlMfll 4ggj|jiA

PLATE 8
All specimens coated and magnified x 31.5

Figs. 1-4. Spathognathodus cf. campbelli Rexroad

ia. Lateral view of specimen X 451. ib. Aboral view of specimen X 451. ic. Oral view of
specimen X 451. 2a. Lateral view of specimen X 435. 2b. Aboral view of specimen X 435.
2c. Oral view of specimen X 435. 3a. Lateral view of specimen X 452. 3b. Oral view of
specimen X 452. 3c. Aboral view of specimen X 452. 4a. Lateral view of specimen X 450.
4b. Oral view of specimen X 450. 4c. Aboral view of specimen X 450.

Fig. 5. Gnathodus simplicatus sp. nov.

a. Lateral view of paratype X 88. b. Oral view of paratype X 88. c. Aboral view of
paratype X 88.

Fig. 6. Gnathodus cuneiformis Mehl and Thomas

a. Lateral view of specimen X 98. b. Oral view of specimen X 98. c. Aboral view of
specimen X 98.

Figs. 7, 8, 12, 13. Spathognathodus cf. cristulus Youngquist & Miller

7a. Lateral view of specimen X 554. 7b. Oral view of specimen X 554. 7c. Aboral view of
specimen X 554. 8a. Lateral view of specimen X 555. 8b. Oral view of specimen X 555.
8c. Aboral view of specimen X 555. 12a. Lateral view of specimen X 556. 12b. Oral view
of specimen X 556. 31a. Lateral view of specimen X 557. 13b. Oral view of specimen X 557.

Figs. 9-1 i. Spathognathodus scitulus (Hinde)

9a. Lateral view of specimen X 391. 9b. Lateral view of specimen X 391. 9c. Oral view of
specimen X 391. gd. Aboral view of specimen X 391. 10a. Lateral view of specimen X 392.
10b. Lateral view of specimen X 392. 10c. Oral view of specimen X 392. iod. Aboral view
of specimen X 392. 11a. Lateral view of specimen X 393. 11b. Lateral view of specimen
X 393. iic. Oral view of specimen X 393. nd. Aboral view of specimen X 393.

Figs. 14-18. Spathognathodus cristulus Youngquist & Miller

14a. Lateral view of specimen X 466. 14b. Lateral view of specimen X 466. 15a. Lateral
view of specimen X 467. 15b. Lateral view of specimen X 467. 15c. Oral view of specimen
X 467. i5d. Aboral view of specimen X 467. 16a. Lateral view of specimen X 468. 16b.
Lateral view of specimen X 468. 16c. Oral view of specimen X 468. i6d. Aboral view of
specimen X 468. 17a. Lateral view of specimen X 464. 17b. Lateral view of specimen X 464.
17c. Oral view of specimen X 464. I7d. Aboral view of specimen X 464. 18a. Lateral view
of specimen X 465. 18b. Lateral view of specimen X 465. 18c. Oral view of specimen
X 465. i8d. Aboral view of specimen X 465.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 8

PLATE 9
All specimens coated and magnified X 31.5

Figs. 1-4. Pseudopolygnathus nodomarginatus (E. R. Branson)

ia. Oral view of specimen X 491. ib. Aboral view of specimen X 491. ic. Lateral view of
specimen X 491. 2a. Oral view of specimen X 489. 2b. Aboral view of specimen X 489.
3c. Lateral view of specimen X 489. 3a. Oral view of specimen X 490. 3b. Aboral view of
specimen X 490. 3c. Lateral view of specimen X 490. 4a. Oral view of specimen X 488.
4b. Aboral view of specimen X 488. 4c. Lateral view of specimen X 488.

Figs. 5-8. Polygnathus lobatus lobatus Branson & Mehl

5a. Oral view of specimen X 378. 5b. Aboral view of specimen X 378. 5c. Lateral view of
specimen X 378. 6a. Oral view of specimen X 376. 6b. Aboral view of specimen X 376.
6c. Lateral view of specimen X 376. 7a. Oral view of specimen X 377. 7b. Aboral view of
specimen X 377. 7c. Lateral view of specimen X 377. 8a. Oral view of specimen X 440.
8b. Aboral view of specimen X 440. 8c. Lateral view of specimen X 440.

Fig. 9. Polygnathus lobatus inflexus subsp. nov.

a. Oral view of holotype X 375. b. Aboral view of holotype X 375. c. Lateral view of
holotype X 375.

Fig. 10. Cavusgnathus ? sp. nov. A.

a. Oral view of specimen X 70. b. Aboral view of specimen X 70. c. Inner lateral view of
specimen X 70. d. Outer lateral view of specimen X 70.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 9

PLATE 10
All specimens coated and magnified x 31.5

Figs. 1-3. Polygnathus inornatus vexatus sub. sp. nov.

ia. Oral view of holotype X 358. ib. Aboral view of holotype X 358. ic. Lateral view of

holotype X 358. 2a. Aboral view of paratype X 359. 2b. Oral view of paratype X 359.

2c. Lateral view of paratype X 359. 3a. Oral view of paratype X 551. 3b. Aboral view of
paratype X 551. 3c. Lateral view of paratype X 551.

Figs. 4-6. Polygnathus inornatus inornatus Branson & Mehl

4a. Aboral view of specimen X 353. 4b. Oral view of specimen X 353. 4c. Lateral view of
specimen X 353. 5a. Aboral view of specimen X 355. 5b. Oral view of specimen X 355.
5c. Lateral view of specimen X 355. 6a. Oral view of specimen X 354. 6b. Aboral view of
specimen X 354. 6c. Lateral view of specimen X 354.

Figs. 7-9. Polygnathus inornatus rostratus subsp. nov.

7a. Aboral view of holotype X 530. 7b. Oral view of holotype X 530. 7c. Lateral view of

holotype X 530. 8a. Aboral view of paratype X 357. 8b. Oral view of paratype X 357.

9a. Aboral view of paratype X 356. 9b. Oral view of paratype X 356. 9c. Lateral view of
paratype X 356.

Bull. By. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 10

PLATE ii
All specimens coated and magnified x 31.5

Figs. 1-4. Polygnathus lacinatus asymtnetricus subsp. nov.

ia. Aboral view of paratype X 360. ib. Oral view of paratype X 360. ic. Lateral view of
paratype X 360. 2a. Aboral view of paratype X 363. 2b. Oral view of paratype X 363.
2C. Lateral view of paratype X 363. 3a. Aboral view of holotype X 361. 3b. Oral view of
holotype X 361. 3c Lateral view of holotype X 361. 4a. Aboral view of paratype X 362.
4b. Oral view of paratype X 362. 4c. Lateral view of paratype X 362.

Figs. 5-7, 11. Polygnathus lacinatus prelobatus subsp. nov.

5a. Oral view of paratype X 372. 5b. Aboral view of paratype X 372. 6a. Oral view of
paratype X 374. 6b. Aboral view of paratype X 374. 7a. Oral view of paratype X 373.
7b. Lateral view of paratype X 373. 11a. Oral view of holotype X 371. nb. Aboral view
of holotype X 371. 11c. Lateral view of holotype X 371.

Figs. 8-10. Polygnathus lacinatus lacinatus Huddle

8a. Oral view of specimen X 370. 8b. Lateral view of specimen X 370. 9a. Oral view of
specimen X 369. 9b. Aboral view of specimen X 369. 9c. Lateral view of specimen X 369.
10a. Aboral view of specimen X 368. 10b. Oral view of specimen X 368. 10c. Lateral view
of specimen X 368 .

Figs. 12-15. Polygnathus lacinatus circaperipherus subsp. nov.

12a. Aboral view of paratype X 367. 12b. Oral view of paratype X 367. 12c. Lateral view
of paratype X 367. 13a. Aboral view of paratype X 365. 13b. Oral view of paratype X 365.
13c. Lateral view of paratype X 365. 14a. Aboral view of holotype X 364. 14b. Oral view of
holotype X 364. 14c. Lateral view of holotype X 364. 15a. Oral view of paratype X 366.
15b. Aboral view of paratype X 366. 15c. Lateral view of paratype X 366.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 11

PLATE 12
All specimens coated and magnified x 31.5

Fig. 1. Polygnathus cf. communis Branson & Mehl

a. Aboral view of specimen X 516. b. Oral view of specimen X 516. c. Lateral view of
specimen X 516.

Figs. 2-5. Polygnathus communis communis Branson & Mehl

2a. Oral view of specimen X 348. 2b. Aboral view of specimen X 348. 2c. Lateral view of
specimen X 348. 3a. Oral view of specimen X 347. 3b. Aboral view of specimen X 347.
3c. Lateral view of specimen X 347. 4a. Aboral view of specimen X 430. 4b. Oral view of
specimen X 430. 4c. Lateral view of specimen X 430. 5a. Oral view of specimen X 346.
5b. Aboral view of specimen X 346. 5c. Lateral view of specimen X 346.

Figs. 6-8, 10. Pseudopolygnathus nodomarginatus (E. R. Branson)

6a. Oral view of specimen X 495. 6b. Aboral view of specimen X 495. 6c. Lateral view of
specimen X 495. 7a. Aboral view of specimen X 493. 7b. Oral view of specimen X 493.
7c. Lateral view of specimen X 493. 8a. Oral view of specimen X 494 showing rounding of
posterior termination. 8b. Aboral view of specimen X 494 showing rounding of posterior
termination. 8c. Lateral view of specimen X 494. 10a. Aboral view of specimen X 492.
10b. Oral view of specimen X 492. 10c. Lateral view of specimen X 492.

Figs. 9, 11. Siphonodella isosticha (Cooper)

9a. Oral view of specimen X 534. 9b. Aboral view of specimen X 534. 11a. Oral view of
specimen X 535. lib. Aboral view of specimen X 535.

Fig. 12. Siphonodella sp. A
a. Aboral view of specimen X 537. b. Oral view of specimen X 537.

Fig. 13. Siphonodella obsoleta Hass

a. Aboral view of specimen X 536. b. Oral view of specimen X 536. c. Lateral view of
specimen X 536.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5.

PLATE 12

PLATE 13
All specimens coated and magnified x 31.5

Figs. 1-3. Taphrognathus - Cavusgnathus transitions

1. Oral view of specimen X 558. 2. Oral view of specimen X 559. 3a. Oral view of specimen
X 560. 3b. Aboral view of specimen X 560. 3c. Outer lateral view of specimen X 560.

Figs. 4, 5. Taphrognathus varians Branson & Mehl

4a. Oral view of specimen X 407. 4b. Aboral view of specimen X 407. 4c. Outer lateral
view of specimen X 407. 4d. Inner lateral view of specimen X 407. 5a. Oral view of specimen
X 408. 5b. Aboral view of specimen X 408. 5c. Outer lateral view of specimen X 408.
5d. Inner lateral view of specimen X 408.

Figs. 6, 7, 13. Cavusgnathus charactus Rexroad

6a. Oral view of specimen X 59. 6b. Aboral view of specimen X 59. 6c. Outer lateral view
of specimen X 59. 6d. Inner lateral view of specimen X 59. 7a. Oral view of specimen X 61.
7b. Aboral view of specimen X 61. 7c. Outer lateral view of specimen X 61 . 7d. Inner lateral
view of specimen X 61. 13a. Oral view of specimen X 62. 13b. Aboral view of specimen
X 62. 13c. Inner lateral view of specimen X 62.

Figs. 8-1 i. Polygnathus bischoffi sp. nov.

8a. Oral view of hypotype X 352. 8b. Aboral view of hypotype X 352. 8c. Lateral view of
hypotype X 352. 9a. Oral view of paratype X 351. 9b. Aboral view of paratype X 351.
9c. Lateral view of paratype X 351. 10a. Oral view of paratype X 350. 10b. Aboral view
of paratype X 350. 10c. Lateral view of paratype X 350. 11a. Oral view of holotype X 349.
11b. Aboral view of holotype X 349. 11c. Lateral view of holotype X 349.

Fig. 12. Cavusgnathus naviculus (Hinde)

a. Oral view of specimen X 65. b. Outer lateral view of specimen X 65. c. Aboral view of
specimen X 65. d. Inner lateral view of specimen X 65.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 13

PLATE 14
All specimens coated and magnified x 31.5

Figs, i, 4-6. Cavusgnathus naviculus (Hinde)

ia. Oral view of specimen X 66. ib. Aboral view of specimen X 66. ic. Inner lateral view
of specimen X 66. id. Outer lateral view of specimen X 66. 4a. Oral view of specimen
X 69. 4b. Aboral view of specimen X 69. 4c. Inner lateral view of specimen X 69. 4d.
Outer lateral view of specimen X 69. 5a. Oral view of specimen X 68. 5b. Aboral view of
specimen X 68. 5c. Inner lateral view of specimen X 68. 5d. Outer lateral view of specimen
X 68. 6a. Oral view of specimen X 67. 6b. Aboral view of specimen X 67. 6c. Inner lateral
view of specimen X 67. 6d. Outer lateral view of specimen X 67.

Fig. 2. Cavusgnathus convexus Rexroad

a. Oral view of specimen X 63. b. Aboral view of specimen X 63. c. Inner lateral view of
specimen X 63. d. Outer lateral views of specimen X 63.

Fig. 3. Cavusgnathus cristatus Branson and Mehl

a. Oral view of specimen X 64. b. Aboral view of specimen X 64. c. Inner lateral view of
specimen X 64. d. Outer lateral view of specimen X 64.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 14

PLATE 15
All specimens coated and magnified x 31.5

Figs. 1-3, 8. Mestognathus bipluti Higgins

ia. Outer aboral lateral view of specimen X 246. ib. Outer lateral oral view of specimen
X 246. ic. Inner lateral oral view of specimen X 246. 2a. Aboral view of specimen X 248.
2b. Outer lateral view of specimen X 248. 2c. Inner lateral view of specimen X 248. 3a.
Outer aboral lateral view of specimen X 247. 3b. Outer lateral oral view of specimen X 247.
3c. Inner lateral oral view of specimen X 247. 8a. Aboral view of specimen X 249. 8b. Inner
oral view of specimen X 249.

Figs. 4-6. Mestognathus neddensis sp. nov.

4a. Aboral view of paratype X 251. 4b. Inner lateral oral view of paratype X 251. 4c. Outer
lateral view of paratype X 251. 5a. Outer aboral lateral view of paratype X 252. 5b. Inner
lateral oral view of paratype X 252. 5c. Outer lateral oral view of paratype X 252. 6a. Aboral
view of holotype X 250. 6b. Inner lateral oral view of holotype X 250. 6c. Outer lateral
view of holotype X 250.

Fig. 7. Mestognathus beckmanni Bischoff

a. Aboral view of specimen X 245. b. Oral view of specimen X 245. c. Outer lateral view
of specimen X 245. d. Inner lateral view of specimen X 245.

Fig. 9. Polygnathus sp.

a. Oral view of specimen X 531. b. Inner lateral view of specimen X 531. c. Aboral view
of specimen X 531.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 15

PLATE 16
All specimens coated and magnified x 31.5

Figs. 1-4. Gnathodus girtyi simplex Dunn

ia. Aboral view of specimen X 108. ib. Oral view of specimen X 108. ic. Outer lateral
view of specimen X 108. id. Inner lateral view of specimen X 108. 2a. Oral view of specimen
X 107. 2b. Aboral view of specimen X 107. 2c. Inner lateral view of specimen X 107.
2d. Outer lateral view of specimen X 107. 3a. Oral view of specimen X no. 3b. Aboral
view of specimen X no. 3c. Inner lateral view of specimen X no. 3d. Outer lateral view
of specimen X no. 4a. Oral view of specimen X in. 4b. Aboral view of specimen X in.
4c. Inner lateral view of specimen X in. 4d. Outer lateral view of specimen X in.

Figs. 5-8. Gnathodus girtyi collinsoni subsp. nov.

5a. Oral view of paratype X 102. 5b. Aboral view of paratype X 102. 5c. Inner lateral
view of paratype X 102. 5d. Outer lateral view of paratype X 102. 6a. Aboral view of
holotype X 99. 6b. Oral view to holotype X 99. 6c. Outer lateral view of holotype X 99.
6d. Inner lateral view of holotype X 99. 7a. Aboral view of paratype X 101. 7b. Oral view
of paratype X 101. 7c. Outer lateral view of paratype X 101. 7d. Inner lateral view of
paratype X 101. 8a. Aboral view of paratype X 100. 8b. Oral view of paratype X 100.
8c. Outer lateral view of paratype X 100. 8d. Inner lateral view of paratype X 100.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 16

2c 3 C

ggm^^ ^gH^ ^^|||tttt[ :^mmk

mum mmm mm*

»1,l*lfj';

/jK^jjjttf| i^^^^k tiMSE^

PLATE 17
All specimens coated and magnified x 31.5

Figs. 1-3. Gnathodus girtyi subsp. nov. A

1 a. Aboral view of specimen X 118. ib. Oral view of specimen X 118. ic. Inner lateral
view of specimen X 118. 2a. Aboral view of specimen X 119. 2b. Oral view of specimen
X 119. 2C. Outer lateral view of specimen X 119. 2d. Inner lateral view of specimen X 119.
3a. Aboral view of specimen X 117. 3b. Oral view of specimen X 117. 3c. Outer lateral
view of specimen X 117. 3d. Inner lateral view of specimen X 117.

Fig. 4. Gnathodus sp.

a. Aboral view of specimen X 138. b. Oral view of specimen X 138. c. Inner lateral view of
specimen X 138. d. Outer lateral view of specimen X 138.

Figs. 5-8. Gnathodus girtyi soniae subsp. nov.

5a. Aboral view of paratype X 115. 5b. Oral view of paratype X 115. 5c. Outer lateral
view of paratype X 115. 5d. Inner lateral view of paratype X 115. 6a. Aboral view of
holotype X 113. 6b. Oral view of holotype X 113. 6c. Outer lateral view of holotype X 113.
7a. Aboral view of paratype X 112. 7b. Oral view of paratype X 112. 7c. Outer lateral
view of paratype X 112. 7d. Inner lateral view of paratype X 112. 8a. Oral view of paratype
X 114. 8b. Aboral view of paratype X 114. 8c. Inner lateral view of paratype X 114.
8d. Outer lateral view of paratype X 114.

Figs. 9-12. Gnathodus girtyi girtyi Hass

9a. Aboral view of specimen X 106. 9b. Oral view of specimen X 106. 9c. Outer lateral
view of specimen X 106. gd. Inner lateral views of specimen X 106. 10a. Aboral view of
specimen X 105. 10b. Oral view of specimen X 105. 10c. Outer lateral view of specimen
X 105. iod. Inner lateral view of specimen X 105. na. Aboral view of specimen X 104.
11b. Oral view of specimen X 104. 11c. Outer lateral view of specimen X 104. nd. Inner
lateral view of specimen X 104. 12a. Aboral view of specimen X 103. 12b. Oral view of
specimen X 103. 12c. Outer lateral view of specimen X 103. i2d. Inner lateral view of
specimen X 103.

Bull. Dr. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE

PLATE 1 8
All specimens coated and magnified x 31.5

Figs, i, 10, n. Gnathodus punctatus (Cooper)

ia. Aboral view of specimen X 132. ib. Oral view of specimen X 132. ic. Outer lateral
view of specimen X 132. 10a. Aboral view of specimen X 131. 10b. Oral view of specimen
X 131. ioc. Inner lateral view of specimen X 131. iod. Outer lateral view of specimen
X 131. 11a. Aboral view of specimen X 133. lib. Oral view of specimen X 133. 11c. Inner
lateral view of specimen X 133. nd. Outer lateral view of specimen X 133.

Figs. 2-5. Gnathodus simplicatus sp. now

2a. Aboral view of holotype X 89. 2b. Oral view of holotype X 89. 2c. Lateral view of
holotype X 89. 3a. Lateral view of paratype X 91. 3b. Oral view of paratype X 91. 4a
Lateral view of paratype X 90. 4b. Oral view of paratype X 90. 5a. Lateral view of
paratype X 415. 5b. Oral view of paratype X 415.

Figs. 6, 8, 13. Gnathodus antetexanus Rexroad & Scott

6a. Aboral view of specimen X 412. 6b. Oral view of specimen X 412. 6c. Outer lateral
view of specimen X 412. 8a. Outer lateral view of specimen X 413. 8b. Oral view of specimen
X 413. 13a. Aboral view of specimen X 414. 13b. Oral view of specimen X 414. 13c. Outer
lateral view of specimen X 414. 13d. Inner lateral view of specimen X 414.

Fig. 7. Gnathodus ? sp. nov.

a. Aboral view of specimen X 92. b. Oral view of specimen X 92. c. Outer lateral view of
specimen X 92.

Fig. 9. Gnathodus avonensis sp. nov.

a. Aboral view of holotype X 411. b. Oral view of holotype X 411. c. Lateral view of
holotype X 411. d. Lateral view of holotype X 411.

Fig. 12. Gnathodus delicatus Branson & Mehl

a. Aboral view of specimen X 87. b. Oral view of specimen X 87. c. Inner lateral view of
specimen X 87. d. Outer lateral view of specimen X 87.

Figs. 14-17. Gnathodus bilineatus (Roundy)

14a. Aboral view of specimen X 94. 14b. Oral view of specimen X 94. 14c. Outer lateral
view of specimen X 94. i4d. Inner lateral view of specimen X 94. 15a. Aboral view of
specimen X 93. 15b. Oral view of specimen X 93. 15c. Inner lateral view of specimen X 93.
I5d. Outer lateral view of specimen X 93. 16a. Aboral view of specimen X 417. 16b. Oral
view of specimen X 417. 16c. Inner lateral view of specimen X 417. i6d. Outer lateral view
of specimen X 417. 17a. Aboral view of specimen X 416. 17b. Oral view of specimen
X 416. 17c. Inner lateral view of specimen X 416. i7d. Outer lateral view of specimen
X 416.

Bull. By. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE ]8

PLATE 19
All specimens coated and magnified x 31.5

Figs. 1-4. Gnathodus symmutatus sp. nov.

ia. Lateral view of paratype X 135. ib. Aboral view of paratype X 135. 2a. Oral view of
para type X 136. 2b. Lateral view of paratype X 136. 2c. Aboral view of paratype X 136.
3a. Lateral view of paratype X 137. 3b. Aboral view of paratype X 137. 4a. Lateral view
of holotype X 134. 4b. Aboral view of holotype X 134. 4c. Oral view of holotype X 134.

Figs. 5-8. Gnathodus homopunctatus Ziegler

5a. Lateral view of specimen X 121. 5b. Lateral view of specimen X 121. 5c. Oral view of
specimen X 121. d. Aboral view of specimen X 121. 6a. Lateral view of specimen X 122.
6b. Lateral view of specimen X 122. 6c. Oral view of specimen X 122. 6d. Aboral view of
specimen X 122. 7a. Lateral view of specimen X 123. 7b. Lateral view of specimen X 123.
7c. Aboral view of specimen X 123. 7d. Oral view of specimen X 123. 8a. Lateral view of
specimen X 120. 8b. Lateral view of specimen X 120. 8c. Aboral view of specimen X 120.
8d. Oral view of specimen X 120.

Figs. 9-12. Gnathodus commutatus (Branson & Mehl)

9a. Lateral view of specimen X 96. 9b. Lateral view of specimen X 96. gc. Aboral view of
specimen X 96. gd. Oral view of specimen X 96. 10a. Lateral view of specimen X 418.
10b. Lateral view of specimen X 418. 10c. Aboral view of specimen X 418. iod. Oral view
of specimen X 418. na. Lateral view of specimen X 95. 11b. Lateral view of specimen
X 95. lie. Aboral view of specimen X 95. nd. Oral view of specimen X 95. 12a. Lateral
view of specimen X 97. 12b. Lateral view of specimen X 97. 12c. Oral view of specimen
X 97. i2d. Aboral view of specimen X 97.

Figs. 13-15. Gnathodus tnononodosus sp. nov.

13a. Lateral view of paratype X 126. 13b. Lateral view of paratype X 126. 13c. Oral view
of paratype X 126. 13d. Aboral view of paratype X 126. 14a. Lateral view of holotype
X 124. 14b. Lateral view of holotype X 124. 14c. Aboral view of holotype X 124. I4d.
Oral view of holotype X 124. 15a. Lateral view of paratype X 125. 15b. Lateral view of
paratype X 125. 15c. Aboral view of paratype X 125. 13d. Oral view of paratype X 125.

Figs. 16-20. Gnathodus nodosus Bischoff

16a. Lateral view of specimen X 128. 16b. Lateral view of specimen X 128. 16c. Aboral
view of specimen X 128. i6d. Oral view of specimen X 128. 17a. Lateral view of specimen
X 509. 17b. Lateral view of specimen X 509. 17c. Aboral view of specimen X 509. I7d.
Oral view of specimen X 509. 18a. Lateral view of specimen X 510. 18b. Lateral view of
specimen X 510. 18c. Aboral view of specimen X 510. i8d. Oral view of specimen X 510.
19a. Lateral view of specimen X 129. 19b. Lateral view of specimen X 129. 19c. Aboral
view of specimen X 129. I9d. Oral view of specimen X 129. 20a. Lateral view of specimen
X 127. 20b. Aboral view of specimen X 127. 20c. Oral view of specimen X 127.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 19

PLATE 20
All specimens coated and magnified x 31.5

Figs. 1-2. Apatognathus chauliodus Varker

ia. Inner lateral view of specimen X 44. ib. Outer lateral view of specimen X 44. 2a. Inner
lateral view of specimen X 550. 2b. Outer lateral view of specimen X 550.

Figs. 3, 4, 6, 7. Apatognathus geminus (Hinde)

3a. Inner lateral view of specimen X 55. 3b. Outer lateral view of specimen X 55. 4a. Inner
lateral view of specimen X 54. 4b. Outer lateral view of specimen X 54. 6a. Outer lateral
view of specimen X 56. 6b. Inner lateral view of specimen X 56. 7a. Inner lateral view of
specimen X 57. 7b. Outer lateral view of specimen X 57.

Fig. 5. Apatognathus various Branson & Mehl
a. Inner lateral view of specimen X 42. b. Outer lateral view of specimen X 42.

Fig. 8. Apatognathus cf. libratus Varker
a. Inner lateral view of specimen X 58. b. Outer lateral view of specimen X 58.

Figs. 9-1 1. Apatognathus scalenus Varker

9a. Inner lateral view of specimen X 48. 9b. Outer lateral view of specimen X 48. 10a. Inner
lateral view of specimen X 49. 10b. Outer lateral view of specimen X 49. 11a. Inner lateral
view of specimen X 47. 11b. Outer lateral view of specimen X 47.

Figs. 12-14, x 7- Apatognathus petilus Varker

12a. Outer lateral view of specimen X 51. 12b. Inner lateral view of specimen X 51. 13a.
Inner lateral view of specimen X 52. 13b. Outer lateral view of specimen X 52. 14a. Inner
lateral view of specimen X 50. 14b. Outer lateral view of specimen X 50. 17a. Inner lateral
view of specimen X 53. 17b. Outer lateral view of specimen X 53.

Figs. 15-16. Apatognathus bladus sp. nov.

15a. Inner lateral view of paratype X 46. 15b. Outer lateral view of paratype X 46. 16a.
Inner lateral view of holotype X 45. 16b. Outer lateral view of holotype X 45.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 20

PLATE 21
All specimens coated and magnified x 31.5

Fig. 1. Neoprioniodus cf. confluens (Branson & Mehl)

a. Lateral view of specimen X 520. b. Aboral view of specimen X 520. c. Oral view of
specimen X 520.

Figs. 2, 8. Neoprioniodus confluens (Branson & Mehl)

2a. Outer lateral view of specimen X 264. 2b. Inner lateral view of specimen X 264. 8a.
Inner lateral view of specimen X 263. 8b. Outer lateral view of specimen X 263.

Fig. 3. Neoprioniodus cf. armatus (Hinde)

a. Inner lateral view of specimen X 283. b. Aboral view of specimen X 283. c. Oral view of
specimen X 283.

Figs. 4-7. Neoprioniodus barbatus (Branson & Mehl)

4. Lateral view of specimen X 259. 5a. Lateral view of specimen X 260. 5b. Aboral view
of specimen X 260. 6. Lateral view of specimen X 262. 7. Lateral view of specimen X 261.

Fig. 9. Neoprioniodus spathatus Higgins
a. Outer lateral view of specimen X 279. b. Inner lateral view of specimen X 279.

Figs, io-ii. Neoprioniodus antespathatus Collinson and Druce

10a. Outer lateral view of specimen X 258. 10b. Inner lateral view of specimen X 258.
11a. Inner lateral view of specimen X 257. lib. Outer lateral view of specimen X 257.

Figs. 12-15. Neoprioniodus peracutus (Hinde)

12a. Inner lateral view of specimen X 273. 12b. Outer lateral view of specimen X 273.

13a. Outer lateral view of specimen X 275. 13b. Inner lateral view of specimen X 275.

14a. Inner lateral view of specimen X 274. 14b. Outer lateral view of specimen X 274.

15a. Outer lateral view of specimen X 272. 15b. Inner lateral view of specimen X 272.

Figs. 16, 17, 20. Neoprioniodus conjunctus (Gunnell)

16a. Inner lateral view of specimen X 265. 16b. Outer lateral view of specimen X 265.
17a. Outer lateral view of specimen X 266. 17b. Inner lateral view of specimen X 266.
20a. Inner lateral view of specimen X 267. 20b. Outer lateral view of specimen X 267.

Fig. 18. Neoprioniodus varians (Branson & Mehl)
a. Outer lateral view of specimen X 281. b. Inner lateral view of specimen X 281.

Fig. 19. Neoprioniodus tulensis (Pander)
a. Outer lateral view of specimen X 280. b. Inner lateral view of specimen X 280.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 21

PLATE 22

All specimens coated and magnified x 31.5

Figs. 1-4. Neoprioniodus cf. camurus Rexroad

ia. Inner lateral view of specimen X 285. ib. Outer lateral view of specimen X 285. 2a.
Inner lateral view of specimen X 287. 2b. Outer lateral view of specimen X 287. 3a. Inner
lateral view of specimen X 284. 3b. Outer lateral view of specimen X 284. 4a. Inner lateral
view of specimen X 286. 4b. Outer lateral view of specimen X 286.

Figs. 5-8. Neoprioniodus montanaensis (Scott)

5a. Outer lateral view of specimen X 271. 5b. Inner lateral view of specimen X 271. 6a.
Inner lateral view of specimen X 269. 6b. Outer lateral view of specimen X 269. 7a. Outer
lateral view of specimen X 268. 7b. Inner lateral view of specimen X 268. 8a. Outer lateral
view of specimen X 270. 8b. Inner lateral view of specimen X 270.

Figs, g, 10, 12. Neoprioniodus scitulus (Branson & Mehl)

9a. Lateral view of specimen X 277. 9b. Lateral view of specimen X 277. 10a. Lateral view
of specimen X 276. 10b. Lateral view of specimen X 276. 12a. Lateral view of specimen
X 278. 12b. Lateral view of specimen X 278.

Fig. 11. Euprioniodina caverna (Collinson & Druce)
a. Outer lateral view of specimen X 83. b. Inner lateral view of specimen X 83.

Fig. 13. Euprioniodina sp. nov. A
a. Inner lateral view of specimen X 86. b. Outer lateral view of specimen X 86.

Fig. 14. Neoprioniodus sp. nov. A
Inner lateral view of specimen X 282.

Fig. 15. Euprioniodina sp.
a. Inner lateral view of specimen X 85. b. Outer lateral view of specimen X 85.

Fig. 16. Euprioniodina microdentata (Ellison)
a. Inner lateral view of specimen X 84. b. Outer lateral view of specimen X 84.

Fig. 17-20. Hindeodus sp.

17a. Outer lateral view of specimen X 191. 17b. Inner lateral view of specimen X 191. 18a.
Outer lateral view of specimen X 189. 18b. Inner lateral view of specimen X 189. 19a. Outer
lateral view of specimen X 188. 19b. Inner lateral view of specimen X 188. 20a. Inner
Literal view of specimen X 190. 20b. Outer lateral view of specimen X 190.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 22

- la 1b^ 2o 2 b 3a . 3b f. ol 4b

12a 12b

13a 13b

] 6a i 6 b

PLATE 23
All specimens coated and magnified x 31.5

Figs. 1-2. Kladognathus clarensis Collinson and Druce

ia. Outer lateral view of specimen X 196. ib. Inner lateral view of specimen X 196. 2a.
Inner lateral view of specimen X 195. 2b. Outer lateral view of specimen X 195.

Figs. 3-6. Kladognathus tnacrodentatus (Higgins)

3a. Inner lateral view of specimen X 197. 3b. Outer lateral view of specimen X 197. 3c.
Oral view of specimen X 197. 4a. Inner lateral view of specimen X 198. 4b. Outer lateral
view of specimen X 198. 4c. Oral view of specimen X 198. 5a. Outer lateral view of specimen
X 199. 5b. Inner lateral view of specimen X 199. 5c. Oral view of specimen X 199. 6a.
Inner lateral view of specimen X 200. 6b. Outer lateral view of specimen X 200. 6c. Oral
view of specimen X 200.

Fig. 7. Magnilaterella ? sp.
a. Inner lateral view of specimen X 447. b. Outer lateral view of specimen X 447.

Figs. 8, 18. Magnilaterella contraria sp. nov.

8a. Inner lateral view of holotype X 553. 8b. Aboral view of holotype X 553. 8c. Outer
lateral view of holotype X 553. 18a. Outer lateral view of paratype X 517. 18b. Inner
lateral view of paratype X 517. 18c. Aboral view of paratype X 517.

Fig. 9, 10. Magnilaterella spp.
9. Inner lateral view of specimen X 244. 10. Inner lateral view of specimen X 242.

Figs. 11-13. Magnilaterella clarkei sp. nov

11. Inner lateral view of paratype X 241. 12. Inner lateral view of holotype X 431. 13a.
Outer lateral view of paratype X 432. 13b. Inner lateral view of paratype X 432.

Figs. 14-17. Magnilaterella complectens (Clarke)

14a. Outer lateral view of specimen X 238. 14b. Aboral view of specimen X 238. 14c. Inner
lateral view of specimen X 238. 15a. Inner lateral view of specimen X 239. 15b. Aboral view
of specimen X 239. 15c. Outer lateral view of specimen X 239. 16a. Outer lateral view of
specimen X 240. 16b. Aboral view of specimen X 240. 16c. Inner lateral view of specimen
X 240. 17a. Outer lateral view of specimen X 237. 17b. Inner lateral view of specimen
X 237. 17c. Aboral view of specimen X 237.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 23

PLATE 24
All specimens coated and magnified x 31.5

Figs. 1-6. Prioniodina prelaevipostica sp. nov.

1. Inner lateral view oi paratype X 333. 2. Inner lateral view of paratype X 332. 3a. Inner
lateral view of paratype X 331. 3b. Oral view of paratype X 331. 3c. Aboral view of
paratype X 331. 4a. Inner lateral view of holotype X 334. 4b. Oral view of holotype X 334.
4c. Aboral view of holotype X 334. 5. Inner lateral view of paratype X 335. 6. Inner
lateral view of paratype X 336.

Fig. 7. Lonchodina obtunda Collinson & Druce

a. Inner lateral view of specimen X 229. b. Oral view of specimen X 229. c. Aboral view of
specimen X 229.

Figs. 8-1 1. Metalonchodina bidentata (Gunnell)

8a. Outer lateral view of specimen X 256. 8b. Inner lateral view of specimen X 256. 9a.
Inner lateral view of specimen X 253. 9b. Outer lateral view of specimen X 253. 9c. Aboral
view of specimen X 253. 10a. Inner lateral view of specimen X 254. 10b. Outer lateral
view of specimen X 254. ua. Outer lateral view of specimen X 255. lib. Inner lateral
view of specimen X 255.

Figs. 12-14. Lonchodina bolbosa Collinson & Druce

12a. Oral view of specimen X 223. 12b. Aboral view of specimen X 223. 13a. Oral view of
specimen X 222. 13b. Aboral view of specimen X 222. 13c. Lateral view of specimen X 222.
14a. Oral view of specimen X 224. 14b. Aboral view of specimen X 224.

Figs. 15, 18. Lonchodina paraclaviger Rexroad

15a. Aboral view of specimen X 233. 15b. Oral view of specimen X 233. 18a. Oral view of
specimen X 232. 18b. Aboral view of specimen X 232.

Fig. 16. Lonchodina paraclarki Hass
a. Aboro-lateral view of specimen X 231. b. Inner lateral view of specimen X 231.

Fig. 17. Lonchodina sp. A

a. Aboro-lateral view of specimen X 424. b. Oral view of specimen X 424.

Fig. 19. Prioniodina latericrescens (Branson & Mehl)
Inner lateral view of specimen X 429.

Figs. 20-23. Lonchodina fur nis hi Rexroad

20a. Inner lateral view of specimen X 227. 20b. Aboral view of specimen X 227. 20c. Oral
view of specimen X 227. 21a. Lateral view of specimen X 226. 21b. Aboral view of specimen
X 226. 21c. Oral view of specimen X 226. 22a. Lateral view of specimen X 225. 22b. Oral
view of specimen X 225. 22c. Aboral view of specimen X 225. 23a. Lateral view of specimen
X 228. 23b. Aboro-lateral view of specimen X 228. 23c. Oral view of specimen X 228.

Bull. By. Mus. nat. Hist. (Geo!. Suppl.) 5

PLATE 24

I'LATE 25
All specimens coated and magnified x 31.5

Fig. 1. Hibbardella (Roundya) sp.
Lateral view of specimen X 423.

Figs. 2-5. Hibbardella (Roundya) barnettana Hass

2a. Aboro-lateral view of specimen X 154. 2b. Lateral view of specimen X 154. 3a. Anterior
view of specimen X 152. 3b. Posterior view of specimen X 152. 4a. Postero-lateral view of
specimen X 151. 4b. Lateral view of specimen X 151. 5a. Lateral view of specimen X 153.
5b. Aboral view of specimen X 153.

Fig. 6. Gen. nov. A sp.
a. Lateral view of specrmen X 409. b. Oral view of specimen X 409.

Fig. 7. Gen. nov. B sp.
a. Lateral view of specimen X 410. b. Aboral view of specimen X 410.

Figs. 8, 9. Plectospat nodus ? sp. nov. A

8a. Inner lateral view of specimen X 313. 8b. Oral view of specimen X 313. 9. Inner lateral
view of specimen X 312.

Figs. 10-12. Plectospathodus ? sp. nov. B

10. Inner lateral view of specimen X 427. n. Inner lateral view of specimen X 428. 12.
Inner lateral view of specimen X 314.

Figs. 13-14. Hibbardella (Hassognathus) separata (Branson & Mehl)

13a. Lateral view of specimen X 150. 13b. Aboral view of specimen X 150. 13c. Posterior
view of specimen X 150. 14. Lateral view of specimen X 149.

Fig. 15. Hibbardella (Hibbardella) sp.

a. Posterior view of specimen X 441. b. Anterior view of specimen X 441.

Figs. 16-18. Hibbardella (Hibbardella) cf. macrodentata Thomas

16a. Posterior view of specimen X 147. 16b. Oral view of specimen X 147. 17a. Lateral view
of specimen X 146. 17b. Posterior view of specimen X 146. 18a. Lateral view of specimen
X 148. 18b. Oral view of specimen X 148. 18c. Posterior view of specimen X 148.

Figs. 19-20. Hibbardella (Hibbardella) acuta Murray & Chronic

19a. Posterior view of specimen X 139. 19b. Anterior view of specimen X 139. 20. Lateral
view of specimen X 422.

Fig. 21. Hibbaradella (Hibbardella) parva sp. nov.
a. Anterior view of holotype X 144. b. Posterior view of holotype X 144.

Fig. 22. Hibbardella (Hibbardella) ortha Rexroad
a. Posterior view of specimen X 143. b. Anterior view of specimen X 143.

Figs. 23-25. Hibbardella (Hibbardella) milleri Rexroad

23a. Anterior view of specimen X 140. 23b. Posterior view of specimen X 140. 24a. Anterior
view of specimen X 141. 24b. Aboral view of specimen X 141. 24c. Posterior view of
specimen X 141. 25a. Anterior view of specimen X 142. 25b. Posterior view of specimen
X 142.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 25

PLATE 26
All specimens coated and magnified x 31.5

Figs. 1-2. Ligonodina osborni sp. nov.

ia. Outer lateral view of holotype X 212. ib. Posterior view of holotype X 212. ic. Inner
lateral view of holotype X 212. 2a. Outer lateral view of paratype X 213. 2b. Posterior
view of paratype X 213. 2c. Inner lateral view of paratype X 213.

Fig. 3. Ligonodina sp. A

3a. Inner lateral view of specimen X 217. 3b. Oral view of specimen X 217. 3c. Aboral view
of specimen X 217.

Figs. 4-6. Ligonodina beata nom. nov.

4. Inner lateral view of specimen X 203. 5a. Inner lateral view of specimen X 201. 5b. Oral
view of specimen X 201. 5c. Aboral view of specimen X 201. 6a. Inner lateral view of
specimen X 202. 6b. Aboral view of specimen X 202.

Fig. 7. Ligonodina ? sp.
Inner lateral view of specimen X 218.

Figs. 8-1 i. Ligonodina magnilaterina sp. nov.

8a. Inner lateral view of paratype X 210. 8b. Outer lateral view of paratype X 210. 9a.
Outer lateral view of paratype X 208. gb. Inner lateral view of paratype X 208. 10a. Inner
lateral view of paratype X 209. 10b. Outer lateral view of paratype X 209. 11a. Outer
lateral view of holotype X 211. lib. Inner lateral view of holotype X 211.

Fig. 12. Ligonodina ? sp.
a. Aboral view of specimen X 219. b. Inner lateral view of specimen X 219.

Figs. 13, 14, 16. Ligonodina roundyi Hass

13a. Inner lateral view of specimen X 216. 13b. Posterior view of specimen X 216. 13c.
Aboral view of specimen X 216. 14a. Postero-lateral view of specimen X 214. 14b. Posterior
view of specimen X 214. 16a. Posterior view of specimen X 215. 16b. Inner lateral view of
specimen X 215. 16c. Aboral view of specimen X 215.

Figs. 15, 17-19. Ligonodina levis Branson & Mehl

15a. Inner lateral view of specimen X 207. 15b. Outer lateral view of specimen X 207.
17a. Inner lateral view of specimen X 206. 17b. Outer lateral view of specimen X 206.
1 8a. Outer lateral view of specimen X 205. 18b. Inner lateral view of specimen X 205.
19a. Inner lateral view of specimen X 204. 19b. Outer lateral view of specimen X 204.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 26

PLATE 27
All specimens coated and magnified x 31.5

Figs. 1-3. Ozarkodina plana (Huddle)

1. Lateral view of specimen X 301. 2. Lateral view of specimen X 300. 3. Lateral view of
specimen X 419.

Figs. 4, 5. Ozarkodina plumula Collinson & Druce

4. Lateral view of specimen X 302. 5a. Lateral view of specimen X 303. 5b. Aboral lateral
view of specimen X 303.

Fig. 6. Ozarkodina curvata Rexroad

a. Outer lateral view of specimen X 289. b. Inner lateral view of specimen X 289.

Figs. 7, 8. Ozarkodina macer (Branson & Mehl)

7. Lateral view of specimen X 305. 8. Lateral view of specimen X 304.

Figs. 9-1 1. Ozarkodina sp.

9. Lateral view of specimen X 307. 10. Lateral view of specimen X 308. 11. Lateral view
of specimen X 306.

Figs. 12, 20, 21. Ozarkodina macra Branson & Mehl

12. Lateral view of specimen X 297. 20. Lateral view of specimen X 296. 21. Lateral view
of specimen X 298.

Fig. 13. Ozarkodina cf. congesta Stauffer
Lateral view of specimen X 288.

Fig. 14. Ozarkodina cf. delicatula (Stauffer & Plummer)
a. Lateral view of specimen X 292. b. Oral view of specimen X 292.

Figs. 15, 19. Ozarkodina delicatula (Stauffer & Plummer)

15a. Lateral view of specimen X 290. 15b. Oral view of specimen X 290. 15c. Aboral view
of specimen X 290. 19a. Lateral view of specimen X 291. 19b. Oral view of specimen
X 291. 19c. Aboral view of specimen X 291.

Figs. 16, 17, 22. Ozarkodina hindei Clarke

16. Lateral view of specimen X 294. 17a. Outer lateral view of specimen X 293. 17b. Inner
lateral view of specimen X 293. 22a. Aboral lateral view of specimen X 295. 22b. Lateral
view of specimen X 295.

Fig. 18. Ozarkodina parva (Huddle)
Lateral view of specimen X 299.

Fig. 23. Ozarkodina compressa Rexroad
Lateral view of specimen X 420.

Fig. 24. Ozarkodina cf. elegans (Stauffer)
Lateral view of specimen X 109.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 27

1 2 3 4

^4* »J^ «>A^ itf6&k# ^yW

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i9b ^^ ^^•■BS55"iP

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^^ ^22^

PLATE 28
All specimens coated and magnified x 31.5

Figs. 1-4. Prioniodina subaequalis (Higgins)
ia. Lateral view of specimen X 344. ib. Aboral view of specimen X 344. ic. Oral view of
specimen X 344. 2a. Lateral view of specimen X 343. 2b. Oral view of specimen X 343.
3a. Aboral view of specimen X 341. 3b. Lateral view of specimen X 341. 3c. Oral view of
specimen X 341. 4. Lateral view of specimen X 342.

Fig. 5. Prioniodina oweni sp. now

a. Lateral view of holotype X 330. b. Oral view of holotype X 330. c. Aboral view of
holotype X 330.

Fig. 6. Prioniodina ? sp. nov.
a. Lateral view of holotype X 345. b. Aboral view of holotype X 345. c. Oral view of
holotype X 345.

Figs. 7-10. Prioniodina stipans (Rexroad)
7a. Lateral view of specimen X 338. 7b. Aboral view of specimen X 338. 7c. Oral view of
specimen X 338. 8a. Lateral view of specimen X 337. 8b. Aboral view of specimen X 337.
8c. Oral view of specimen X 337. 9a. Lateral view of specimen X 339. 9b. Aboral view of
specimen X 339. gc. Oral view of specimen X 339. 10a. Lateral view of specimen X 340.
10b. Aboral view of specimen X 340. 10c. Oral view of specimen X 340.

Figs. 11-12. Prioniodina laevipostica (Rexroad & Collinson)
11. Inner lateral view of specimen X 317. 12a. Outer lateral view of specimen X 316. 12b.
Inner lateral view of specimen X 316.

Fig. 13. Prioniodina eireica (Collinson & Druce)
Inner lateral view of specimen X 315.

Fig. 14. Hindeodella sp. nov.
a. Oral view of specimen X 186. b. Lateral view of specimen X 186.

Figs. 15-17. Hindeodella croka Collinson & Druce
15. Oral view of specimen X 164. 16. Oral view of specimen X 162. 17. Oral view of
specimen X 163.

Figs. 18-20. Hindeodella hibbardi Collinson & Druce
18. Lateral view of specimen X 167. 19. Lateral view of specimen X 168. 20. Lateral view
of specimen X 169.

Figs. 21, 26. Hindeodella montanaensis (Scott)

21. Lateral view of specimen X 175. 26. Lateral view of specimen X 176.

Figs. 22-24, 30-3 1 - Hindeodella ibergensis (Bischoff)

22. Lateral view of specimen X 171. 23. Lateral view of specimen X 170. 24. Lateral view
of specimen X 173. 30. Lateral view of specimen X 172. 31. Lateral view of specimen
X 174.

Figs. 25, 28. Hindeodella antecomplex Collinson & Druce
25. Lateral view of specimen X 157. 28. Lateral view of specimen X 156.

Fig. 27. Hindeodella tenuis Clarke
Lateral view of specimen X 187.

Fig. 29. Hindeodella cf. croka Collinson & Druce
Oral view of specimen X 165

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 28

PLATE 29
All specimens coated and magnified x 31.5

Figs. 1-2. Angulodtis sp. nov. D

ia. Lateral view of specimen X 41. ib. Oral view of specimen X 41. ic. Aboral view of
specimen X 41. 2a. Lateral view of specimen X 40. 2b. Oral view o'f specimen X 40. 2c.
Aboral view of specimen X 40.

Figs. 3-4. Angulodus sp. nov. C.

3a. Lateral view of specimen X 39. 3b. Oral view of specimen X 39. 3c. Aboral view of
specimen X 39. 4a. Lateral view of specimen X 38. 4b. Oral view of specimen X 38. 4c.
Aboral view of specimen X 38.

Fig. 5. Angulodus sp. nov. B.
a. Lateral view of specimen X 37. b. Aboral view of specimen X 37.

Figs. 6-7, 9-10. Hindeodella subtilis Ulrich & Bassler

6a. Lateral view of specimen X 180. 6b. Oral view of specimen X 180. 7a. Lateral view of
specimen X 177. 7b. Oral view of specimen X 177. 9. Lateral view of specimen X 178.
10a. Lateral view of specimen X 179. 10b. Oral view of specimen X 179.

Fig. 8. Angulodus walrathi (Hibbard)
Lateral view of specimen X 36.

Figs, ii, 13-15. Hindeodella secarata Collinson & Druce

11. Lateral view of specimen X 184. 13. Lateral view of specimen X 181. 14. Lateral view
of specimen X 182. 15. Lateral view of specimen X 183.

Fig. 12. Hindeodella sp.

a. Lateral view of specimen X 445. b. Oral view of specimen X 445. c. Aboral view of
specimen X 445.

Figs. 16-17. Hindeodella corpulenta Branson & Mehl

16a. Lateral view of specimen X 160. 16b. Postero-lateral view of specimen X 160. 16c.
Aboral view of specimen X 160. 17a. Aboral view of specimen X 161. 17b. Lateral view of
specimen X 161. 17c. Postero-lateral view of specimen X 161.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 29

la 2a

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PLATE 30
All specimens coated and magnified x 31.5

Fig. 1. Gnathodus semiglaber Bischoff

a. Oral view of specimen X 421. b. Aboral view of specimen X 421. c. Lateral view of
specimen X 421.

Figs. 2, 8. Gnathodus punctatus - Gnathodus semiglaber transition
2. Oral view of specimen X 521. 8. Oral view of specimen X 525.

Figs. 3, 7, 9-17. Pseudopolygnathus cf. longiposticus Branson & Mehl

3a. Aboral view of specimen X 443. 3b. Oral view of specimen X 443. 7a. Aboral lateral
view of specimen X 448. 7b. Oral view of specimen X 448. 9. Aboral view of specimen
X 442. 10. Oral view of specimen X 442. 11. Oral view of growth stages of specimen X 522.
12. Oral view of growth stages of specimen X 523. 13. Oral view of growth stages of specimen
X 433. 14. Oral view of growth stages of specimen X 434. 15. Oral view of growth stages of
specimen X 547. 16. Oral view of specimen X 449. 17a. Oral view of specimen X 545.
17b. Aboral view of specimen X 545.

Figs. 4, 5. Gnathodus sp.

4a. Oral view of specimen X 424. 4b. Aboral view of specimen X 424. 4c. Lateral view of
specimen X 424. 5a. Aboral view of specimen X 425. 5b. Oral view of specimen X 425.
5c. Lateral view of specimen X 425.

Fig. 6. Gnathodus delicatus Branson & Mehl

a. Oral view of specimen X 426. b. Aboral view of specimen X 426. c. Lateral view of
specimen X 426.

Fig. 18. Gnathodus bilineatus (Roundy) transitional from G. punctatus (Cooper)
a. Oral view of specimen X 439. b. Aboral view of specimen X 439.

Fig. 19. Pseudopolygnathus triangulus cf. pinnatus Voges
a. Aboral view of specimen X 502. b. Oral view of specimen X 502.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 30

PLATE 31
All specimens coated and magnified x 31.5

Fig. 1. Hindeodella undata Branson & Mehl
Lateral view of specimen X 185.

Fig. 2. Apatognathus sp.
Inner lateral view of specimen X 318.

Fig. 3. Hibbardella (Hassognathus) ? sp.
Lateral view of specimen X 319.

Fig. 4, 16. Ligonodina tenuis Branson & Mehl

4. Lateral view of specimen X 320. 16. Lateral view of specimen X 321.

Figs. 5, 11. Magnilaterella spp.

5. Inner lateral view of specimen X 322. 11. Aboral inner lateral view of specimen X 323.

Fig. 6. Hibbardella (Hibbardella) abnormis Branson & Mehl
Lateral view of specimen X 508.

Fig. 7, 10. Hindeodus alatoides (Rexroad & Burton)
7. Lateral view of specimen X 193. 10. Lateral view of specimen X 192.

Fig. 8. Hindeodus imperfectus (Rexroad)
Lateral view of specimen X 194.

Fig. 9. Ligonodina tulensis (Pander)
Lateral view of specimen X 328.

Fig. 12. Spathognathodus scitulus subsp. nov.
a. Oral view of specimen X 390. b. Aboral view of specimen X 390. c. Lateral view of
specimen X 390.

Fig. 13. Cavusgnathus unicornis Youngquist & Miller
a. Aboral view of specimen X 329. b. Lateral view of specimen X 329.

Fig. 14. Lonchodina transitans Collinson & Druce
Lateral view of specimen X 234.

Fig. 15. Kladognathus mehli (Rexroad)
Inner lateral view of specimen X 524.

Fig. 17. Hindeodella brevis Branson & Mehl
Lateral view of specimen X 514.

Figs. 18, 19. Hindeodella cooperi (Elias)
18. Lateral view of specimen X 158. 19. Lateral view of specimen X 159.

Fig. 20. Siphonodella sp.
Oral view of specimen X 539.

Fig. 21. Polygnathus sp.
a. Oral view of specimen X 130. b. Aboral view of specimen X 130.

Fig. 22. Apatognathus sp. nov. A.
a. Inner lateral view of specimen X 43. b. Outer lateral view of specimen X 43.

Fig. 23. Gnathodus girtyi turritus Collinson & Druce
a. Lateral view of specimen X 116. b. Aboral view of specimen X 116. c. Oral view of
specimen X 116.

Fig. 24. Geniculatus sp.
Lateral view of specimen X 327.

Figs. 25-26. Magnilaterella robusta Rexroad & Collinson
25. Inner lateral view of juvenile specimen X 528. 26. Inner lateral view of specimen X 529.

Fig. 27. Apatognathus porcatus (Hinde)
Inner lateral view of specimen X 220.

Bull. Br. Mus. nat. Hist. (Geol. Suppl.) 5

PLATE 31

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